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Originally appearing in Volume V20, Page 793 of the 1911 Encyclopedia Britannica.
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PARASITIC DISEASES. It has long been recognized that various specific pathological conditions are due to the presence and action of parasites (see PARASITISM) in the human body, but in recent years the part played in the causation of the so-called infective diseases by various members of the Schizomycetes—fission fungi—and by Protozoan and other animal parasites has been more widely and more thoroughly investigated (see BACTERIOLOGY). The knowledge gained has not only modified our conception of the pathology of these diseases, but has had a most important influence upon our methods of treatment of sufferers, both as individuals and .as members of communities. For clinical and other details of the diseases mentioned in the following classification, see the separate articles on them; the present article is concerned mainly with important modern discoveries as regards aetiology and pathology. In certain cases indeed the aetiology is still obscure. Thus, according to Guarnieri, and Councilman & Calkins, there is associated with vaccinia and with small-pox a Protozoan parasite, Cytoryctes variolae, Guar. This parasite is described as present in the cytoplasm of the stratified epithelium of the skin and mucous membranes in cases of vaccinia, but in the nuclei of the same cells in cases of variola or small-pox, whilst it is suggested that there may be a third phase of existence, not yet demonstrated, in which it occurs as minute spores or germs which are very readily carried in dust and by air currents from point to point. In certain other conditions, such as mumps, dengue, epidemic dropsy, oriental sore—with which the Leishman-Donovan bodies (Helcosoma tropicum, Wright) are supposed to be closely associated (see also Kdla-dzar below)—verruga, framboesia or yaws—with which is commonly associated a spirochaete (Castellani) and a special micrococcus (Pierez, Nicholls)—and beri-beri, the disease may be the result of the action of specific micro-organisms, though as yet it has not been possible to demonstrate any aetiologica relationship between any micro-organisms found and the special disease. Such diseases as haemoglobinuric fever or black-water fever, which are also presumably parasitic diseases, are probably associated directly with malaria; this supposition is the more probable in that both of these are recognized as occurring specially in those patients who have been weakened by malaria. The following classification is based partly upon the biological relations of the parasites and partly on the pathological phenomena of individual diseases: A.—Diseases due to Vegetable Parasites. I.—To SCHIZOMYCETES, BACTERIA OR FISSION FUNGI. I. Caused by the Pyogenetic Micrococci. Suppuration and Septicaemia. Erysipelas. Infective Endocarditis. Gonorrhoea. 2. Caused by Specific Bacilli. (a) Acute Infective Fevers. Cholera. Infective Meningitis. Typhoid Fever. Influenza. Malta Fever. Yellow Fever and Weil's Disease. Relapsing Fever. Diphtheria. Plague. Tetanus. Pneumonia. (b) More Chronicinfective Diseases (tissue parasites). Tuberculosis. Glanders. Leprosy. II.—To HIGHER VEGETABLE PARASITES. Actinomycosis, Madura Foot, Aspergillosis and other Mycoses. B.—Diseases due to Animal Parasites.' I.—To PROTOZOA. Malaria.' Khla-Azar. Amoebic Dysentery. Tsetse-fly Disease. Haemoglobinuric Fever. Sleeping Sickness. Syphilis. II.—To OTHER ANIMAL PARASITES. Filariasis, &c. C.—Infective Diseases in which an organism has been found, but has not finally been connected with the disease. Hydrophobia. Scarlet Fever. D.—Infective Diseases not yet proved to be due to micro-organisms. Small-pox. Mumps. Typhus Fever. Whooping Cough, &c. Measles A.—Diseases due to Vegetable Parasites. I.—To SCHIZOMYCETES, BACTERIA OR FISSION FUNGI. 1. Caused by the Pyogenetic Micrococci. Suppuration and Septicaemia.—It is now recognized that although nitrate of silver, turpentine, castor oil, perchloride of mercury and certain other chemical substances are capable of producing suppuration, the most common causes of this condition are undoubtedly the so-called pus-producing bacteria. Of these perhaps the most important are the staphylococci (cocci arranged like bunches of grapes), streptococci (cocci arranged in chains), and pneumococci, though certain other organisms not usually associated with pus-formation are undoubtedly capable of setting up this condition, e.g. Bacillus pyocyaneus, Bacillus coli communis, and the typhoid bacillus. These organisms (the products of which, by chemical irritation, stimulate the leucocytes to emigration) bring about the death and digestion of the tissues and fluids (which no longer " clot ") with which they come in contact, pus (matter) being thus formed: this accumulates in the tissues, in the serous cavities, or even on mucous surfaces; septicaemia or blood-poisoning, secondary infection of tissues and organs at a distance from the original site of infection, or pyaemia, with the formation of secondary abscesses, may thus be set up. In septicaemia the pus-forming organisms grow at the seat of introduction, and produce special poisons or toxins, which, absorbed into the blood, give rise to symptoms of fever. From the point of introduction, however, the organisms may be swept away either by the lymph or by the blood, and carried to positions in which they set up further inflammatory or suppurative changes. In the streptococcal inflammations spreading by the lymph channels appears to be specially prevalent. In the blood the organisms, if in small numbers, are usually destroyed by the plasma, which has a powerful bactericidal action; should they escape, however, they are carried without multiplication into the capillaries of the general circulation, of the lung, or of the liver, where, being stopped, they may give rise to a second focus of infection, especially if at the point of impaction the vitality of the tissues is in any way lowered. Unless the blood is very much impoverished, its bactericidal action is usually sufficiently powerful to bring about the destruction of anything but comparatively large masses of pyogenetic organisms. This bactericidal power, however, may be lost; in such case the pus-forming organisms may actually multiply, a general haemic infection resulting. Should micro-organisms be conveyed by the veins to the heart, and there be deposited on an injured valve, an infective endocarditis is the result; from such a deposit numerous organisms may be continuously poured into the circulation. Simple thrombi or clots may also become infected with micro-organisms. Fragments of these, washed away, may form septic plugs in the vessels and give rise to abscesses at the points where they become impacted. A distinction must be drawn between sapraemia and septicaemia. In sapraemia the toxic products of saprophytic organisms are absorbed from a gangrenous or necrotic mass, from an ulcerating surface. or from a large surface on which saprophytic organisms are living and feeding on dead tissues: for example, we may have such a condition in the clots that sometimes remain after childbirth on the inner surface of the wall of the womb. So long as no micro-organisms follow the toxins, the condition is purely sapraemic, but should any organisms make their way into and multiply in the blood, the condition becomes one of septicaemia. The term pyaemia isusually associated with the formation of fresh secondary foci of suppuration in distant parts of the body. If the primary abscess occurs in the lungs, the secondary or metastatic abscesses usually occur in the vessels of the general or systemic circulation, and less frequently in other vessels of the lung. When the primary abscess occurs in the systemic area, the secondary abscess occurs first in the lung, and less frequently in the systemic vessels; whilst if the primary abscess be in the portal area (the veins of the digestive tract), the secondary abscesses are usually distributed over the same area, the lungs and systemic vessels being more rarely affected. Infective Endocarditis.—Acute malignant or ulcerative endocarditis occurs in certain forms of septicaemia or of pyaemia. It is brought about by the Streptococcus pyogenes (see Plate II. fig. 2), the pneumococcus, or the Staphylococcus pyogenes aureus (see Plate I. fig. 4), or, more rarely, by the gonococcus, the typhoid bacillus or the tubercle bacillus, as they gain access to acute or chronic valvular lesions of the heart. The aortic and mitral valves are usually affected, the pulmonary and tricuspid valves much more rarely, though Washbourn states that the infective form occurs on the right side more frequently than does simple endocarditis. A rapid necrosis of the surface of the valve is early followed by a deposition of fibrin and Ieucocytes on the necrosed tissue; the bacteria, though not present in the circulating blood during life, are found in these vegetations which break down very rapidly; ulcerative lesions are thus formed, and fragments of the septic clot (i.e. the fibrinous vegetations with their enclosed bacteria) are carried in the circulating blood to different parts of the body, and, becoming impacted in the smaller vessels, give rise to septic infarcts and abscesses. The ulceration of the valves, or in the first part of the aorta, may be so extensive that aneurysm, or even perforation, may ensue. In certain cases of streptococcic endocarditis the use of antistreptococcic serum appears to have been attended with good results. Sir A. Wright found that the introduction of vaccines prepared from the pus-producing organisms after first lowering the opsonic index almost invariably, after a very short interval, causes it to rise. He found, too, that the vaccine is specially efficacious when it is prepared from the organisms associated with the special form of suppuration to be treated. Whenever the opsonic index becomes higher under this treatment the suppurative process gradually subsides: boils, acne, pustules, carbuncles all giving way to the vaccine treatment. The immunity so obtained is attributed to the increased activity of the serum as the result of the presence of an increased amount of opsonins. Further, Bier maintains that a passive congestion and oedema induced by constriction of a part by means of a ligature or by a modification of the old method of cupping without breaking the skin appears to have a similar effect in modifying localized suppurative processes, that is processes set up by pus-producing bacteria. Wright holds that this treatment is always more effective when the opsonic index is high and that the mere accumulation of oedematous fluid in the part is sufficient to raise the opsonic index of that fluid and therefore to bring about a greater phagocytic activity of the leucocytes that are found in such enormous numbers in the neighbourhood of suppurative organisms and their products. Erysipelas.—In 1883 Fehleisen demonstrated that in all cases of active erysipelatous inflammation a streptococcus or chain of micrococci (similar to those met with in certain forms of suppuration) may be found in the lymph spaces in the skin. The multiplying streptococci found in the lymph spaces form an active poison, which, acting on the blood-vessels, causes them to dilate; it also " attracts " leucocytes, and usually induces proliferation of the endothelial cells lining the lymphatics. These cells—perhaps by using up all available oxygen—interfere with the growth of the streptococcus and act as phagocytes, taking up or devouring the dead or weakened micro-organisms. Both mild and severe phlegmonous cases of erysipelas are the result of the action of this special coccus, alone, or in combination with other organisms. It has been observed that changes when injected, without the gonococci, into the anterior cancerous and other malignant tumours appear to recede under chamber of the eye of the rabbit. an attack of erysipelas, and certain cases have been recorded by both Fehleisen and Coley in which complete cessation of 2. Caused by Specific Bacilli. growth and degeneration of the tumour have followed such an (a) Acute Infective Fevers. attack. As the streptococcus of erysipelas can be isolated and Cholera.—In x884 Koch, in the report of the German Cholera Commission in Egypt and India, brought forward overwhelming evidence in proof of his contention that a special bacterium is the causal agent of cholera; subsequent observers in all countries in which cholera has been met with have confirmed Koch's observation. The organism described is the " comma " bacillus or vibrio, one of the spirilla, which usually occurs as a slightly curved rod x to 211 in length and 0.5 to a•6µ in thickness. These comma-shaped rods occur singly or in pairs; they may be joined together to form circles, half-circles, or " S "-shaped curves (see Plate II. fig. 3). In cultivations in specially prepared media they may be so grouped as to form long wavy or spiral threads, each of which may be made up of ten, twenty, or even thirty, of the short curved vibrios; in the stools of cholera patients, especially during the earlier stages of the disease, they are found in considerable numbers; they may also be found in the contents of the lower bowel and in the substance of the mucous membrane of the lower part of the small intestine, especially in the crypts and in a-id around the epithelium lining the follicles. It is sometimes difficult, in the later stages of the disease, to obtain these organisms in sufficiently large numbers to be able to distinguish them by direct microscopic examination, but by using the Dunbar-Schottelius method they can be detected even grown in pure culture in broth, it was thought by these observers that a subcutaneous injection of such a cultivation might be of value in the treatment of cancerous tumours. No difficulty was experienced in setting up erysipelas by inoculation, but in some cases the process was so acute that the remedy was more fatal than the disease. The virulence of the streptococcus of erysipelas, as pointed out by Fehleisen and Coley, is greatly exalted when the coccus is grown alongside the Bacillus prodigiosus and certain other saprophytic organisms which flourish at the body-temperature. It is an easier matter to control the action of a non-multiplying poison, even though exceedingly active, than of one capable, under favourable conditions, of producing an indefinite amount of even a weaker poison. The erysipelatous virus having been raised to as high a degree of activity as possible by cultivating it along with the Bacillus prodigiosus--the bacillus of " bleeding " bread—in broth, is killed by heat, and the resulting fluid, which contains a quantity of the toxic substances that set up the characteristic erysipelatous changes, is utilized for the production of an inflammatory process—which can now be accurately controlled, and which is said to be very beneficial in the treatment of certain malignant tumours. The accurate , when present in small numbers. A quantity of faintly alkaline determination of the aetiology of erysipelas has led to the meat broth, with 2 % of peptone and % common salt, is inoculated with some of the contents of the intestine, and is placed in an adoption of a scientific method of treatment of the disease. incubator at a temperature of 35° C. for about twelve hours, when, The Streptococcus erysipelatis is found, not specially in the zone if any cholera bacilli are present, a delicate pellicle, consisting in which inflammation has become evident, but in the tissues outside this zone: in fact, the streptococci appear to be most numerous in the lymphatics of the tissues in which there is little change. Before the appearance of any redness there is a dilatation of the lymph spaces with fluid, and the tissues become slightly oedematous. As soon, however, as the distension of vessels and the emigration of leucocytes, with the accompanying swelling and redness, become marked, the streptococci disappear or are imperfectly stained—they are undergoing degenerative changes—the inflammatory " reaction " apparently being sufficient to bring about this result. advance? This theory was tested on animals, and it was found that the application of iodine, oil of mustard, cantharides and similar rubefacients would prevent the advance of certain micro-organisms. This treatment was applied to erysipelatous patients with the most satisfactory result, the spread of the disease being prevented when-ever the zone of inflammation was extended over a sufficiently wide area. The mere " ringing " of the red patch by nitrate of silver or some other similar irritant, as at one time recommended, is not sufficient: it is necessary that the reaction should extend for some little distance beyond the zone to which the streptococci have already advanced. Gonorrhoea.—A micro-organism, the gonococcus, is the cause of gonorrhoea. It is found in the pus of the urethra and in the conjunctiva lying between the epithelial cells, where it sets up considerable irritation and exudation; it occurs in the fluid of joints of patients affected with gonorrhoeal arthritis; also in the pleuritic effusion and in the vegetations of gonorrhoeal endocarditis. It is a small diplococcus, the elements of which are flattened or slightly concave disks apposed to one another; these, dividing transversely, sometimes form tetrads. They are found in large numbers, usually in the leucocytes, adherent to the epithelial cells or lying free. They stain readily with the basic aniline dyes, but lose this stain when treated by Gram's method. The gonococcus is best grown on human blood-serum mixed with agar (Wertheim), though it grows on ordinary solidified blood-serum or on blood-agar. Like the pneumococcus, it soon dies out, usually before the eighth or ninth day, unless reinoculations are made. It forms a semi-transparent disk-like growth, with somewhat irregular margins, or with small processes running out beyond the main colony. It acts by means of toxins, which have been found to set up irritative almost entirely of short " comma " bacilli, appears on the surface. If the growth be allowed to continue, the bacilli increase in length, but after a time the pellicle is gradually lost, the cholera organisms being overgrown, as it were, by the other organisms. In order to obtain a pure culture of the cholera bacillus, remove a small fragment of the young film, shake it up thoroughly in a little broth, and then make gelatine-plate cultivations, when most characteristic colonies appear as small greyish or white points. Each of these, when examined under a low-power lens, has a yellow tinge; the margins are wavy or crenated; the surface is granular and has a peculiar ground-glass appearance; around the growing colony liquefaction takes place, and the colony gradually sinks to the bottom of the liquefying area, which now appears as a clear ring. The organism grows very luxuriantly in milk, in which, however, If it were possible to set up the same reaction outside the 1 it gives rise to no very noticeable alteration; its presence can only advancing streptococci might not a barrier be raised against their ~ be recognized by a faint aromatic and sweetish smell, which can scarcely be distinguished from the aromatic smell of. the milk itself, except by the most practised nose. The cholera bacillus may remain alive in water for some time, but it appears to be less resistant than many of the putrefactive and saprophytic organisms. It grows better in a saline solution (brackish water) than in perfectly fresh water; it flourishes in serum and other albuminous fluids, especially when peptones are present. Its power of forming poisonous substances appears to vary directly with the amount and nature of the albumen present in the nutrient medium; and though it grows most readily in the presence of peptone, it appears to form the most virulent poison when grown in some form or other of crude albumen to which there is not too free access of oxygen. From the experiments carried out by Koch, Nicati and Rietsch, and Macleod, there appears to be no doubt that the healthy stomach and intestine are not favourable breeding-grounds for the cholera bacillus. In the first place, it requires an alkaline medium for its full and active development, and the add found in a healthy stomach seems to exert an exceedingly deleterious influence upon it. Secondly, it appears to be incapable of developing except when left at rest, so that the active peristaltic movement of the intestine interferes with its development. Moreover, it forms its poison most easily in the presence of crude albumen. It is interesting to note what an important bearing these facts have on the personal and general spread of cholera. Large quantities of the cholera bacillus may be injected into the stomach of a guinea-pig without any intoxicative or other symptoms of cholera making their appearance. Further, healthy individuals have swallowed, without any ill effect, pills containing the dejecta from cholera cases, although cases are recorded in which "artificial" infection of the human subject has undoubtedly taken place, whilst, as Metchnikoff demonstrated, very young rabbits, deriving milk from mothers whose mammary glands have been smeared with a culture of the cholera vibrio, soon succumbed, suffering from the classical symptoms of this disease. If, however, previous to the injection of the cholera bacillus the acidity of the stomach be neutralized by an alkaline fluid, especially if at the same time the peristaltic action of the intestine be paralysed by an injection of morphia, a characteristic attack of cholera is developed, the animal is poisoned, and in the large intestine a considerable quantity of fluid faeces containing numerous cholera bacilli may be found. There appear to be slight differences in the cholera organisms found in connexion with different outbreaks, but the main characteristics are preserved throughout, and are sufficiently distinctive to mark out all these organisms as belonging to the cholera group. Amongst the known predisposing causes of cholera are the incautious use of purgative medicines, the use of unripe fruit, insufficient food and intemperance. These may be all looked upon as playing the part of the alkaline solution in altering the composition of the gastric juices, and especially as setting up alkaline fermentation in the stomach and small intestine; beyond this, however, the irritation set up may bring about an accumulation of inflammatory serous fluid, from the albumens of which, as we have seen, the cholera organism has the power of producing very active toxins. The part played by want of personal cleanliness, overcrowding and unfavourable hygienic conditions may be readily under-stood if it be remembered that the cholera bacillus may grow outside the body. The number of cases in which epidemics of cholera have been traced to the use of drinking-water contaminated with the discharges from cholera patients is now consider-able. The more organic matter present the greater is the virulence of water so contaminated; and the addition of such water to milk has, in one instance at least, led to an outbreak. If cholera dejecta be sprinkled on moist soil or damp linen, and kept at blood-heat, the bacillus multiplies at an enormous rate in the first twenty-four or thirty-six hours; but, as seen in the Dunbar-Schottelius method, at the end of three or four days it is gradually overcome by the other bacteria present, which, growing strongly and asserting themselves, cause it to die out. The importance of this saprophytic growth in the propagation of the disease can scarcely be over-estimated. Water which contains an ordinary amount of organic and inorganic matter in solution does not allow of the multiplication of this organism, which may soon die out; but when organic matter is present in excess, as at the margin of stagnant pools and tanks, development occurs, especially on the floating solid particles. This bacillus grows at a temperature of 3o° C. on meat, eggs, vegetables and moistened bread; also on cheese, coffee, chocolate and dilute sugar solutions. In some experiments carried out by Cartwright Wood and the writer in connexion with the passage of the cholera organism through filters it remained alive in the charcoal filtering medium for a period of at least forty-two days, and probably for a couple of months. It must be remembered that cholera bacilli are gradually overcome or overgrown by other organisms, as only on this supposition can the immunity enjoyed by certain regions, even after the water and soil have been contaminated, provided that no fresh supply is brought in " to relight the torch," be explained. In most of the regions in which cholera remains endemic the wells are merely dug-out pits beneath the slightly raised houses, and are open for the reception of sewage and excreta at all times. These dejecta contain organic material which serves as a nutriment on which infective organisms, derived from the soil and ground-water, may flourish. Not only dejecta, but also the rinsings from soiled linen and utensils used by cholera patients should be removed as soon as possible, "without allowing them to come into contact with the surface of the soil, with wells," or with vegetables and the like. The discovery of Koch's co;n;na bacillus has soaltered our conceptions of the aetiology of this disease that we now study the conditions under which the bacillus can multiply and be disseminated, instead of concerning ourselves with the cholera itself as some definite entity. Telluric agencies become merely secondary factors, the dissemination of the disease by winds from country to country is no Ionger regarded as being possible, whilst the spread of cholera epidemics along the lines of human intercourse and travel is now recognized. The virulent bacillus requires the human organism to carry it from those localities in which it is endemic to those in which epidemics occur. The epidemiologist has come to look upon the study of the cholera organism and the conditions under which it exists as of more importance than mere local conditions, which are only important in so far as they contribute to the propagation and distribution of the cholera bacillus, and he knows that the only means of preventing its spread is the careful inspection of everything coming from cholera-stricken regions. He also recognizes that the herding together of people of depressed vitality, under unhygienic and often filthy conditions, in quarantine stations or ships, is one of the surest means of promoting an epidemic of the disease; that attention should be confined to the careful isolation of all patients, and to the disinfection of articles of clothing, feeding utensils, and the like; that the comma bacillus can only be driven out of rooms by means of light and fresh air; that thorough personal, culinary and house-hold cleanliness is necessary; that all water except that known to be pure should be carefully boiled; and that all excess, both in eating and drinking, should be avoided. The object of the physician in such cases must be first to isolate as completely as possible all his cholera patients, and then to get rid of all predisposing causes in the patients themselves, causes which have already been indicated in connexion with the aetiology of the disease. Attention has frequently been drawn to the fact that patients who have lived for some time in a cholera region, or who have already suffered from an attack of cholera, appear to enjoy a partial immunity against the disease. Haffkine, working on the assumption that the symptoms of cholera are produced by a toxin formed by the cholera organism, came to the conclusion that, by introducing first a modified and then a more virulent poison directly into the tissues under the skin, and not into the alimentary canal, it would be possible to obtain a certain insusceptibility to the action of this poison. He found that for this purpose the cholera bacillus, as ordinarily obtained in pure culture from the intestinal canal, is too potent for the preliminary inoculation, but is not sufficiently active for the second, if any marked protection is to be obtained. By allowing the organism to grow in a well-aerated culture the virulence is gradually diminished, and this virulence, once abolished, does not return even when numerous successive cultures are made on agar or other nutrient media. On the other hand, by passing the cholera bacillus successively through the peritoneal cavities of a series of about thirty guinea-pigs, he obtains a virus of great activity; this activity is soon lost on agar cultivations, and it is necessary, from time to time, again to pass the bacillus through guinea-pigs, three or four passages now being sufficient to reinforce the activity. From these two cultures the vaccines are prepared as follows: The surface of a slant agar tube is smeared with the modified cholera organism. After this has been allowed to grow for twenty-four hours, a small quantity of sterile water is poured into the tube, and the surface-growth is carefully scraped off and made into an emulsion in the water; this is then poured off, and the process is repeated until the whole of the growth has been removed. The mixture is made up with water to a bulk of 8 c.c., so that if t c.c. is injected the patient receives i of a surface-growth ; it is found that this quantity, when injected subcutaneously into a guinea-pig, gives a distinct reaction, but does not cause necrosis of the tissues. If the vaccine is to be kept for any length of time, the emulsion is made with o•5 % carbolic acid solution, prepared with carefully sterilized water, and the mixture is made up to 6 c.c. instead of 8 c.c., since the carbolic acid appears to interfere slightly with the activity of the virus. The stronger virus is prepared in exactly the same way. The preliminary injection, which is made in the left flank, is followed by a rise in temperature and by local reaction. After three or four hours there is noticeable swelling and some pain; and after ten hours a rise in temperature, usually not very marked, occurs. These signs soon disappear, and at the end of three or four days the second injection is made, usually on the opposite side. This is also followed by a rise of temperature, by swelling, pain and local redness: these, however, as before, soon pass off, and leave no ill effects behind. A guinea-pig treated in this fashion is now immune against some eight or ten times the lethal dose of cholera poison, and, from all statistics that can be obtained, a similar protection is conferred upon the human being. Pfeiffer found that when a small quantity of the cholera vibrio is injected into the peritoneal cavity of a guinea-pig highly immunized against cholera by Haffkine's or a similar method, these vibrios rapidly become motionless and granular, then very much swollen and finally " dissolve." This is known as Pfeiffer's reaction. A similar reaction may be obtained when a quantity of a culture of the cholera vibrio mixed with the serum derived from a guinea-pig immunized against the cholera vibrio, or from a patient convalescent from the disease, is injected into the peritoneal cavity of a guinea-pig not subjected to any preliminary treatment; and, going a step further, it was found that the dissolution of the cholera vibrio is brought about even when the mixture of vibrio and serum is made in a test tube. On this series of experiments as a foundation, the theory of acquired immunity has been reared. Evidence has been collected that spirilla, almost identical in appearance with the cholera bacillus, may be present in water and in healthy stools, and that it is in many cases almost impossible to diagnose between these and the cholera bacillus; but although these spirilla may interfere with the diagnosis, they do not invalidate Koch's main contention, that a special form of the comma bacillus, which gives a complete group of reactions, is the cause of this disease, especially when these reactions are met with in an organism that comes from the human intestine. Typhoid Fever.—Our information concerning the aetiology of typhoid fever was largely increased during the last twenty years of the 19th century. In 188o Eberth and Klebs independently, and in 1882 Coats, described a bacillus which has since been found to be intimately associated with typhoid fever. This organism (Plate II. fig. 4) usually appears in the form of a short bacillus from 2 to 31110 length and o•3 to 0.51t in breadth; it has slightly rounded ends and is stained at the poles; it may also occur as a somewhat longer rod more equally stained through-out. Surrounding the young organism are numerous long and well-formed flagella, which give it a very characteristic appearance under the microscope. At present there is no evidence that the typhoid bacillus forms spores. These bacilli are found in the adenoid follicles or lymphatic tissues of the intestine, in the mesenteric glands, in the spleen, liver and kidneys, and may also be detected even in the small lymphoid masses in the lung and in the post-typhoid abscesses formed in the bones, kidneys, or other parts of the body; indeed, it is probable that they were first seen by von Recklinghausen in 1871 in such abscesses. They undoubtedly occur in the dejecta of patients suffering from typhoid fever, whilst in recent years it has been demonstrated that they may also be found in the urine. It is evident, therefore, that the urine, as well as the faeces, may be the vehicle by means of which the disease has been unwittingly spread in certain otherwise inexplicable outbreaks of typhoid fever, especially as the bacillus may be present in the urine when the acute stage of the disease has gone by, and when it has been assumed that, as the patient is convalescent, he is no longer a focus from which the infection may be spread. Easton and Knox found typhoid bacilli in the urine of 21% of a series of their typhoid patients. In 1906 Kayser demonstrated what had previously been suspected, that the typhoid bacilli may persist for considerable periods in the bile duct and gall bladder, whence they pass into the intestinal tract and are discharged with the evacuations. Patients in whom this occurs are spoken of as " typhoid carriers." They become convalescent and except that now and again they suffer from slight attacks of diarrhoea they appear to be perfectly healthy. It has been observed, however, especially during these attacks of diarrhoea, that typhoid bacilli may be found in the faeces. Curiously enough the bacilli are as virulent as are those isolated when the disease is at its height. Hence these typhoid carriers are exceedingly dangerous centres of infection, and as women act as " carriers " much more frequently than do men, although, as is well known, typhoid fever attacks men much more frequently than women, the facilitiesfor the distribution of the disease are great, as women so frequently act as laundresses, cooks, housemaids, nurses and the like. Frosch states that out of 6708 typhoid patients 310 excreted bacilli for more than lo weeks after convalescence; 144 of these were no longer infective. at the end of three months; 64 had ceased to be infective at the end of a year, and toe at the end of three and a-half years; further back than this no authentic records could be obtained but from a critical examination of the histories of 25 such carrier cases he was convinced that 14 had been continuously infective for from four to nine years. Dr Donald Greig, in 1908, reported a. case in which the patient appears to have been a typhoid carrier for fifty-two years from the time of convalescence. Frosch pointed out. what has now been fully confirmed, that the bacilli in these cases though often present in the faeces in enormous numbers may disappear and again reappear from time to time and that a continuous series of examinations is necessary before a convalescent patient can be acquitted of being a " typhoid carrier." In this connexion it is interesting to note that Blumenthal and Kayser have discovered typhoid bacilli in the interior of gall-stones. Drs Alexander and J. C. G. Ledingham, examining the 90 female patients and attendants in a Scottish asylum in which, during some four or five years, 31 cases of typhoid had occurred in small groups in which the source of infection could not be traced to any recognized channel, found amongst them three " typhoid carriers." The importance of such a discovery amongst asylum patients may be readily understood when the careless and uncleanly habits of insane patients are borne in mind. As it has been demonstrated that' the typhoid bacillus is found, not merely in the lymphatic tissue but, in 75 % of the cases, actually circulating in the blood, the appearance of the bacillus in the secretions and excretions may be readily understood. There can be little doubt that typhoid bacilli are not, as is very frequently assumed, present merely in the lymphatic glands and in the spleen (see Nate II. fig. 5) : they may be found in almost any part of the lymphatic system, in lymph spaces, in the connective tissues, where they appear to give rise to marked proliferation of the endothelial cells, and especially in the various secreting organs. It is probable that the proliferation often noticed in the minute portal spaces in the liver, in cases of typhoid fever, is simply a type of a similar proliferation going on in other parts and tissues of the body. It was for long assumed that the typhoid bacillus could multiply freely in water, but recent experiments appear to indicate that this is not the case, unless a much larger quantity of soluble organic matter is present than is usually met with in water. The fact, however, that the organism may remain alive in water is of great importance; and, as in the case of cholera, it must be recognized that certain of the great epidemics of typhoid or enteric fever have been the result of "water-borne infection." The bacillus, a facultative parasite, grows outside the body, with somewhat characteristic appearances and reactions: it flourishes specially well on a slightly acid medium; in the presence of putrefactive organisms which develop strongly alkaline products it may gradually die out, but it appears to retain its vitality longer in the presence of acid-forming organisms. It may, however, be stated generally that after a time the typhoid bacillus becomes weakened, and may even die out, in the presence of rapidly growing putrefactive organisms. In distilled water it may remain alive for a considerable period—five or six weeks, or even longer. It grows on all the ordinary nutrient media. It does not coagulate milk; hence it may grow luxuriantly in that medium without giving rise to any alteration in its physical characters; contaminated milk, therefore, is specially dangerous affording as it does an excellent vehicle for the dissemination of the typhoid bacillus which may also be conveyed by food and even by water. To food the bacillus is readily conveyed by flies, on their limbs or by the proboscis, which become infected by the excrement on which they crawl and feed. The observations of physicians working amongst the British troops in South Africa afford abundant evidence that the typhoid bacillus may also be carried along with dust from excreta to fresh patients, for although these bacilli die very rapidly when they are desiccated, they remain alive sufficiently long to enable them to multiply and flourish when again brought into contact with moist food, milk, &c. When inoculated on potato, careful examination will reveal the fact that certain almost invisible moist patches are present; these are made up of rapidly multiplying typhoid bacilli. The typhoid bacillus grows in gelatin, especially on the surface, somewhat like the bacillus coli communis, but with a less luxuriant growth. This organism, when taken from young broth cultures twelve to twenty-four hours old—during the period at which flagella are best seen—and examined microscopically, exhibits very lively movements. When, as pointed out by Gruber and Durham, blood-serum, in certain dilutions, from a case of typhoid fever is added to such a culture, the broth, at first turbid, owing to the suspended and moving micro-organisms, gradually becomes clear, and a deposit is formed which is found to be made up of masses or clumps of typhoid bacilli which have lost their motility. This reaction is so characteristic and definite, that when the mixture is kept under examination under the microscope, it is quite possible to follow the slowing-down movement and massing together of the organisms. It is found, moreover, that normal diluted blood-serum has no such effect on the bacilli. This property of the blood-serum is acquired at such an early date of the disease—sometimes even at the end of the first week—and occurs with such regularity, that typhoid fever may now actually be diagnosed by the presence or absence of this " agglutinating " property in the blood. If serum taken from a patient supposed to be suffering from typhoid fever, and diluted with saline solution to r in ro, to i in 50, or in still greater dilution, causes the bacilli to lose their motility and to become aggregated into clumps within an hour, it may be concluded that the patient is suffering from typhoid fever; if this agglutination be not obtained with a dilution of r in 10, in from 15 to 30 minutes, experience has shown that the patient is not suffering from this disease. Certain other diseases, such as cholera, give a similar specific serum reaction with their specific organisms. These sera have, in addition, a slight common action—a general agglutinating power—which, however, is not manifested except in concentrated solutions, the higher dilutions failing to give any clumping action at all, except with the specific bacillus associated with the disease from which the patient, from whom the serum is taken, is suffering. Wright and Semple, working on Haffkine's lines, introduced a method of vaccination against typhoid, corresponding somewhat to that devised by Haffkine to protect against cholera. They first obtained a typhoid bacillus of fairly constant virulence and of such strength and power of multiplication that an agar culture of 24 hours' growth when divided into four, and injected hypodermically, will kill four fairly large guinea-pigs, each weighing 350 to 400 grammes. A similar culture emulsified in bouillon or saline solution and killed by heating for five minutes at 60° C. is a vaccine sufficient for from four to twenty doses. In place of the agar culture a bouillon culture heated for the same period may be used as the vaccine. In either case the vaccine is injected under the skin of the loin "well above the crest of the ileum. This injection is usually followed by local tenderness and swelling within three or four hours, and swelling and tenderness in the position of the nearest lymphatic glands, marked malaise, headache, a general feeling of restlessness and discomfort and a rise of temperature. The blood of a patient so treated early causes agglutination of typhoid bacilli and acts on these bacilli much as does cholera serum in Pfeiffer's reaction. At the end of ten days a second and stronger dose is given. After each injection there is, according to Wright, a "negative phase" during which the patient is somewhat more susceptible to the attacks of the typhoid bacillus. This negative phase soon passes off and a distinct positive or protected phase appears. The practical outcome of this is that wherever possible a patient who is going into a typhoid infected area should be vaccinated some little time before he sets out. There seems to be no doubt that if this be done a very marked, though not complete, protection is conferred. For a time the agglutinative and lytic powers of the serum continue to rise and the patient so vaccinated is far less susceptible to the action of the typhoid bacillus. It is recorded in favour of this method of treatment that of 4502 soldiers of the Indian army inoculated 0.98% contracted typhoid, while of 25,851 soldiers of the same army who were not inoculated over 21°/s (2.54) contracted typhoid. Similarly, at Ladysmith, of the whole of the besieged soldiers only 1705 had been inoculated, but of these only 2 % contracted typhoid, whilst of 10,529 uninoculated men 14% were attacked. Wright, who has been indefatigable in carrying out and watching this method of treatment, has been able to accumulate statistics dealing with 49,600 individuals —of these 8600 were inoculated, and 24 % contracted typhoid, 12 % of these succumbing to the disease. Of the 41,000 uninoculated men 51% contracted the disease, 21 % of those attacked succumbing. Mediterranean or Malta Fever.—Until comparatively recently, Mediterranean fever was looked upon as a form or typhoidfever, which in certain respects it resembles; the temperature curve, however, has a more undulatory character, except in the malignant type, where the temperhure remains high throughout the course of the attack. According to Hughes, this disease is widely distributed in the countries bordering upon the Mediterranean south of latitude 46° N., and along the Red Sea littoral. Analogous forms of fever giving a " specific " serum reaction with the micrococcus of this disease are also met with in parts of India, China, Africa and America. The Micrococcus melitensis vel Brucei ( 1887), which is found most abundantly in the enlarged spleen of the patient suffering from Malta fever, is a very minute organism (o•33µ in diameter), ovoid or nearly round, arranged in pairs or in very short chains. If a drop of the blood taken directly from the spleen be smeared over the surface of agar nutrient medium, minute transparent colourless colonies appear; in thirty-six hours these have a slight amber tinge, and in four or five days from their first appearance they become opaque. These colonies, which flourish at the temperature of the human blood, cease to grow at the room-temperature except in summer, and if kept moist, soon die at anything below 6o° F., though when dried they retain their vitality for some time. As the organism grows and multiplies in broth there is opacity of the medium at the end of five or six days, this being followed by precipitation, so that a comparatively clear supernatant fluid remains. It grows best on media slightly less alkaline than human blood; it is very vigorous and may resist desiccation for several weeks. This organism is distinctly pathogenetic to monkeys, and its virulence may be so increased that other animals may be affected by it. Though unable to live in clean or virgin soil, it may lead a saprophytic existence in soil' polluted with faecal matter. Hughes maintains that the " virus " leaves the body of goats and of man along with the faeces and urine. The importance of this in ambulatory cases is very evident, especially when it is remembered that goats feeding on grass, &c. which has come in contact with such urine are readily infected. It seldom appears to be carried for any considerable distance. Infection is not conveyed by the sputum, sweat, breath or scraping of the skin of patients, and infected dust does not seem to play a very important part in producing the disease. Hughes divides the fever into three types. In the malignant form the onset is sudden, there are headache, racking pain over the whole body, nausea and sometimes vomiting; the tongue is foul, coated and swollen, and the breath very offensive; the temperature may continue for some time at 103° to 105° F. The stools in the ,diarrhoea which is sometime'§ present may be most offensive. At the end of a few days the lungs become congested and pneumonic, the pulse weak, hyperpyrexia appears, and death ensues. A second type, by far the most common, is the "undulatory" type, in which there is remittent pyrexia, separated by periods in which the patient appears to be improving. These pyrexial curves, from one to seven in number, average about ten days each, the first being the longest,—eighteen to twenty-three days. In an' intermittent type, in which the temperature-curve closely resembles the hectic pyrexial curve of phthisis or suppuration, the "undulatory" character is also marked. A considerable number of toxic symptoms make their appearance—localized neuritis, synovitis, anaemia, emaciation, bronchial catarrh, weakness of the heart, neuralgia, profuse night-sweats and similar conditions. Patients otherwise healthy usually recover, even after prolonged attacks of the disease, but the mortality amongst patients suffering from organic mischief of any kind may be comparatively high. The diagnosis from malaria, phthisis, rheumatic affections and pneumonia may, in most cases, be made fairly easily, but the serum agglutinating reaction (first demonstrated by Wright in 1897) with cultures of the Micrococcus melitensis, corresponding to the typhoid reaction with the typhoid bacillus, is sometimes the only trustworthy feature by which a diagnosis may be made between this fever and the above-mentioned diseases. About 50% of the goats in Malta give a positive agglutinative reaction and about ro% excrete milk which contains the micrococcus. Sir David Bruce, in his investigations on the tsetse fly disease, pointed out that certain wild animals although apparently in good health might serve as reservoirs for, or storehouses of, the N'gana parasite. He was therefore quite prepared to find that the Micrococcus melitensis might similarly be " stored " in an animal which might show but slight, if any, manifestations of Malta fever. Iilications as to the direction in which to look were given in the following fashion. There was a strike amongst the dairymen supplying the barracks in Malta and it became necessary to replace the goat's milk in the dietary of the troops by condensed milk. What followed ? In the first half of the year 1906 there had been 144 cases (in 1905 there had been 750 cases), in the second half after the alteration of the milk supply, only 32 cases were recorded and in 1907, 7 cases during the whole year. In the navy during the same period there were, in 1905, 498 cases, in 1906, 248 cases and, from January to September 1907, not a single case. The most common method of infection is by the ingestion of milk, but the milk when handled may also give rise to infection through finding its way into cuts, bruises, &c. In the goat the disease is of an extremely mild character, the clinical symptoms, which are present for two or three days only, being easily overlooked. In spite of this the goat is highly susceptible to the infection either by the various methods of inoculation or as the result of feeding with contaminated or infected material. The micrococcus is often found in the circulating blood from which it may be excreted along with the urine and faeces. In time, however, it disappears, first from the general circulation and most of the viscera, persisting longest in the spleen, kidneys and lymphatic glands. In the later stages of the disease the micrococcus is found in the milk even after it has disappeared from the above glands. It is during this stage that the milk of the goat is so dangerous, as now and again it may contain an enormous number of the specific micrococcus varying " within wide limits from day to day," although bearing " no relationship to the severity of the infection, air temperature, &c.; the presence of the Micrococcus melitensis in the milk appears to be merely the result of a mechanical flushing of the mammary glands by means of which the cocci multiplying therein are removed." As pointed out by the Mediterranean Fever Commission the micrococcus of Malta fever from its vantage ground in the milk may make its way to ordinary ice-creams and to native cheeses, in which it appears to retain its full virulence. Monkeys are especially susceptible to this disease, contracting it readily when they are fed with milk from an infected goat. In 1905 an interesting experiment was, unintentionally, carried out. An official of the United States Bureau of Animal Industry visiting Malta in the summer of that year purchased a herd of 61 milch-goats and four billy goats. These were shipped via Antwerp to the United States. On arrival at Antwerp the goats were transferred to a quarantine station, where they remained for five days and were then consigned by steamer to New York. On board the SS. " Joshua Nicholson," which took the goats from Malta to Antwerp, were twenty-three officers and men; ten out of the twenty-three were afterwards traced. One was found to have been infected by M. melitensis at an unknown date, and' eight had subsequently suffered from febrile attacks, five yielding conclusive evidence of infection by M. melitensis. It is interesting to note, however, that two men who boiled the milk before drinking it, and an officer and a cabin-boy who disliked the milk and did not drink it at all, came off scot free. These cases taken by themselves might leave the question some-what open, as there was a possibility that the men attacked might have been in contact with Infected patients in Malta. A far more conclusive case was the following. A woman at the quarantine station at Athenia, N. J., U.S.A., who partook freely of the mixed milk from several goats, over a considerable period, suffered from a typical attack of Mediterranean fever some nine or ten weeks after the goats had been landed in America. In this case " contact " with and other modes of exposure to infection by human patients could all be eliminated. It may be held then that the M. melitensis leads a more or less passive existence in the body of the Maltese goat, only exercising its full pathogenic action when it gains entrance to the human body. There is some slight evidence that the Micrococcus melitensis may remain alive with its virulence unimpaired even when taken up by the mosquitoes Acartomyia and Stegomyia, and again in the common blood-sucking fly, Stomoxys, for a short period, four or five days. It can be recovered for a longer period and still in a fairly virulent condition from the excreta of these insects. In spite of this, trans-mission of the disease by these insects, though apparently possible, does not appear to be of very frequent occurrence. Inoculation with a vaccine prepared from the Micrococcus melitensis appears to exert a protective influence for a period of about four months, after which time there is a marked diminution in the immunity conferred by this vaccination. Relapsing Fever.—The specific cause of relapsing fever (famine fever) appears to be the Spirillum Obermeieri, an organism which occurs in the blood (during the febrile stages) of patients suffering from this disease. Between the febrile stages are periods of intermission, during which the spirillum disappearsfrom the blood and, apparently, retires to the spleen. This disease, in epidemic form, follows in the footsteps of famine and destitution, specially affecting young people between the ages of fifteen and twenty; it seldom attacks children under five years of age, but when it attacks patients over thirty it assumes a very virulent form. In monkeys inoculated with blood containing the Spirillum Obermeieri the first symptoms appear between the second and sixth days. In the human subject this incubation period may last as long as three weeks; then comes an attack of fever, which continues for about a week, and is followed by a similar period of apparent convalescence, on which ensues a pyrexial relapse, continuing about half as long as the first. The spirilla, the cause of this disease, are fine spirals with pointed ends, three or four times as long as the diameter of a red blood corpuscle. Although it has as yet been found impossible to cultivate these spirilla outside the body, human beings, and monkeys injected with blood containing them, contract the disease; and in monkeys it has been found that during the period before the relapse the spirilla have made their way into the cells of the spleen. As yet little is known as to the mode of development of these organisms, and of the method of their transmission from one patient to another, but it is thought that, as in the case of malaria and the tsetse-fly disease, they may be carried by bloodsucking insects. Relapsing fever is distinguished from typhoid fever by its sudden onset, and by the distinct intermissions; and from influenza by the enlargement of . the spleen and liver. The most satisfactory method of diagnosis is the examination of the blood for the presence of the spirillum during the febrile stage. The post-mortem appearances are those of a toxic (bacterial) poisoning. Curious infarction-like masses, in which are numerous spirilla, are found in the spleen; in the liver there is evidence of acute interstitial hepatitis, with cloudy swelling of the liver cells; and similar changes occur in the kidney. Fatty degeneration of the heart and voluntary muscles may also he met with. Plague.—During recent years opportunities for the study of plague have unfortunately been only too numerous. In patients suffering from this disease, a micro-organism, capable of leading either a saprophytic life or a parasitic existence in the human body, and in some of the lower animals, was described independently by Kitasato and Lowson and by Yersin, 1894, in Hong-Kong. It is a short moderately thick oval bacillus, with rounded ends, which stain deeply, leaving a clear band in the centre (see Plate II., fig. 7). It thus resembles the short diphtheria bacillus and the influenza bacillus. Certain other forms are met with—long rods and " large oval bacilli, pear-shaped or round, imperfectly stained pale involution forms "—but the above is the most characteristic. It grows readily on most media at the temperature of the body, but, like the glanders bacillus, soon loses its virulence in cultivations. It may be obtained in pure cultures from the lymph glands, and from the abscesses that are formed in the groin or other positions in which the glands become enlarged and softened. It may also be found in the spleen and in the blood, and, in the case of patients suffering from the pneumonic form of the disease, even in the lungs and in the sputum. It has also been found in the faeces and urine. (It is very important that these excretions from plague patients should always be most carefully disinfected.) This organism, when obtained in pure culture and inoculated into rats, mice, guinea-pigs or rabbits, produces exactly the same symptoms as does material taken fresh from the softened glands. The symptoms are local swelling, enlargement and softening of the lymphatic glands, and high fever. The difficulty of explaining the spread of plague, at one time apparently almost insuperable, has at last been overcome, as it has been found that although the acute pneumonic plague is undoubtedly highly contagious, the spread of the bubonic and septicaemic forms could not be explained on the same hypothesis. As the pneumonic form is met with in only about 2.5% of the whole of the cases, transmission by direct contagion seems to be an utterly inadequate explanation. In the autumn of 1896, when the plague broke out in India, and those dealing with the outbreak came to the conclusion that certain houses were centres of infection, it was noticed that these houses were most infective at night, and that they might actually be centres of infection although uninhabited; indeed the infection seemed to spread to houses between which and the infected house there appeared to be no intercommunication of any kind. This seemed to be inexplicable except on the assumption that the infective agent, the Bacillus pestis, was, in some way or other, carried by animals. It had already been noted that rats disappeared from plague-stricken houses, many dying before the appearance of the plague in the human population. Simond, noting these conditions, suggested that the plague bacillus might be transmitted by the flea from rat to rat and from rat to man. Although he was not able to demonstrate this connexion he indicated a line of research to other observers, who, as knowledge accumulated, were able to complete each link in the chain of infection. The plague bacillus having been found in the rat, the next step was to demonstrate its presence in the flea, and living plague germs were found in the stomachs of fleas inhabiting plague-infected houses. Several species seem to be able to transmit this germ, but in none of them does the plague bacillus appear to undergo any special development —alternation of generations or the like—as in the case of the protozoon of malaria in its passage from and to the mosquito and the human subject —it simply passes unchanged through the alimentary canal of the flea, is excreted in the faeces, and is carried into the wound made by the epipharynx-mandibles of the flea. At least three species of animals, two rats and the human subject, and three species of fleas are involved in this chain. The rat fleas are Pulex cheopis found in India, and Ceratophyllus fasciatus, the rat flea of northern Europe, and Pulex irritans, the common flea, all of which have the power of transmitting the disease. In India of course the Pulex cheopis, usually solely associated with rats, seems to play the most prominent part. The two rats involved are the Mus decumanus, or brown rat, which is' found in the sewers and develops the plague first, and the Mus rattus, the common black house-rat. From the sewer-rat the house-rat is infected, and from the house-rat man. Under ordinary conditions rat fleas do not attack the human subject, but, as the rats are attacked by plague and die, the infected fleas, starve out as it were, leave them and transfer their attentions to other animals and the human subject, infecting many of those they bite. Colonel Bannerman maintains that this infection takes place in the majority of cases, by this chain of transmission, and that there is no evidence that the excreta of these rats infect food or contaminate the soil. Colonel Lamb, summarizing the experimental evidence on this question, writes: " 1. Close contact of plague-infected animals with healthy animals, if fleas are excluded, does not give rise to an epizootic among the latter. As the godowns (experimental huts) were never cleaned out, close contact includes contact with faeces and urine of infected animals, and contact with and eating of food contaminated with faeces and urine of infected animals as well as with pus from open plague ulcers; (2) close contact of young, even when suckled by plague-infected mothers, did not give the disease to the former; (3) if fleas are present, then the epizootic, once started, spreads from animal to animal, the rate of progress being in direct proportion to the number of fleas present; (4) an epizootic of plague may start without direct contact of healthy animal and infected animal; (5) the rat flea can convey plague from rat to rat; (6) infection can take place without any contact with contaminated soil; (7) aerial infection is excluded." The experiments lead to the conclusion that fleas and fleas alone, are the transmitting agents of infection. Bannerman gives in concise form similar evidence in relation to naturally infected native houses. Infection is carried from place to place by fleas, usually on the body or in the clothing of the human being. Such fleas, fed on infected blood, may remain alive for three weeks, and of this period, we are told, may remain infective for fifteen days. At the first opportunity these fleas forsake the human host and return to their natural host the rat. In most of the epidemics there is a definite sequence of events. First the brown rats are attacked, then the black rats,then the human subject, and Colonel Lamb suggests that after the rat disappears the flea starves for about three days and then attacks the human subject. Then comes the incubation period of plague, three days. Following this is the period of average duration of the disease, five or six days. This time-table, he says, corresponds to the period—when the epidemics are at their height—that intervenes between the maximum death-rate in rats and the maximum death-rate in man, about ten to fourteen days. This history of the connexion between the flea, the rat, and the human subject reads almost like a fairy tale, but it is now one of the well-authenticated and sober facts of modern medicine. In India, where the notions of cleanliness are somewhat different from those recognized in Great Britain, most of the conditions favourable to the spread of the plague bacillus are of the most perfect character. This organism may pass into the soil with faeces; it may there remain for some time, and then be taken into the body of one of the lower animals, or of man, and give rise to a fresh outbreak. Kitasato and Yersin were both able to prove that soil and dust from infected houses contain the bacillus, that such bacillus is capable of inducing an attack of plague in the lower animals, and that flies fed on the dejecta or other bacillus-containing material, die, and in turn contain bacilli which are capable of setting up infection. Hankin claims that ants may carry the plague to and from rats, and so to the human being. It has already been mentioned that the organism rapidly loses its virulence when cultivated outside the body; on the other hand, on being passed through a series of animals its virulence gradually increases. Thus may be explained the fact that in most outbreaks of plague there is an early period during which the death-rate is very low; after a time the percentage mortality is enormously increased, the virulence of the disease being very great and its course rapid. There seem to be notable differences in the degree of susceptibility of different races and different individuals, and those who have passed safely through an attack appear to have acquired a marked degree of immunity. Two methods of treatment, both of which seem to have been attended with a certain degree of success, are now being tried. Haffkine, who was the first to produce a vaccine for the treatment of cholera, prepared a vaccine of a somewhat similar type for the treatment of plague. For this the Bacillus pestis is cultivated in flasks of bouillon; to this small drops or particles of ghee (Indian butter) are added; these form centres around which the organisms may develop. As the organisms multiply they grow down into the broth, but gradually becoming fewer in number as the floating mass on the surface is left, they fine down to a point and so come to resemble stalactites. These are broken off, from time to time, by shaking,. others immediately beginning to form in their place. This may go on for six weeks. The flask with its contents is then well shaken and heated in a water bath to 70° C. for from one to three hours. On testing by culture the fluid should now be sterile, i.e. no bacilli should remain alive, and the fluid, ready for use, may be injected into the subcutaneous tissues of the arm in a dose of from 3 cc. for a man and 2 to 21 cc. for a woman, children receiving relatively small amounts. A rise of temperature, followed by malaise and headache, which pass off in about 24 hours, is soon noted, and some local swelling and redness appear at the seat of injection. The Indian Plague Commission were satisfied that the use bf this vaccine diminishes the incidence of attacks of plague, and that, although it does not confer a complete immunity against the disease, the case mortality is lowered. They are of opinion also that protection is not conferred at once, but Lieut.-Colonel Bannerman states that the protection is immediate and lasts for six or even twelve months. In the official report (Annual Report of the Sanitary Commissioner with the Government of India) for 1904 occurs the following: " That its value is great is certain, not only does it largely diminish the danger of plague being contracted, but, if it fails to prevent the attack, the probability of a fatal event is reduced by one-half." This method of treatment, however, is of no avail in the case of patients already attacked; for such cases Yersin's serum treatment must be called in. Various other vaccines have been described, but all consist of some form of killed or attenuated bacilli, and the results attained do not vary very greatly. Yersin, who first demonstrated the plague bacillus also devised the method of preparing an " antipest serum." A horse was inoculated repeatedly, at intervals, and with gradually increasing doses of living plague bacilli. It was afterwards found that cultures sterilized by heat served equally well for this inoculation of the horse and of course were much more easily worked with. This process of preparation may have to be continued for from six months to a year. The horse is then bled and from the clot the serum is separated, care being taken to determine by injection of the blood into mice that no living bacilli have by accident made their way into, and remained in, the horse's blood. The serum is not considered to be sufficiently active until a drop and a half will protect the mouse against a dose of living bacilli fatal to a control mouse in from 48 to 6o hours. When this serum is injected in sufficiently large doses subcutaneously in mild cases, and sub-cutaneously and intravenously (Lancet, 1903, 1. 1287) in more severe cases in doses of 150 to 300 cc. the results seem to be excellent, especially when the serum is injected into the tissues around the bubo or swellings formed in this disease. Calmette and Salimbeni used the serum in 142 cases in the Oporto outbreak. Amongst these they had a mortality of under 15%, whilst amongst 72 patients not so treated the death-rate was over 63 %. This serum kills the bacilli and at the same time neutralizes the toxin formed during the course of the disease. The best results are obtained when large doses are given, and when the serum injected subcutaneously is thrown into the area in which the lymph flows towards the bubo. As in the case of the diphtheria antitoxic serum joint pains and rashes may follow its exhibition, but no other ill effects have been noted. Pneumonia.—The case in favour of acute lobar pneumonia being an infective disease was a very strong one, even before it was possible to show that a special organism bore any aetiological relation to it. In 1880, Friedlander claimed that he had isolated such an organism, but the pneumo-bacillus then described appears to be inactive as compared with the pneumococcus isolated by Fraenkel and Talamon. This latter organism which is usually found in the sputum, is an encapsuled diplococcus. Grown on serum or agar over which sterile blood has been smeared, it occurs as minute, glistening, rather prominent points, almost like a fine spray of water or dew. When the organism is cultivated in broth the capsule disappears, and chains of diplococci are seen. It resembles the influenza bacillus in a most remarkable manner. It may be found, in almost every case of pneumonia, in the " rusty " or " prune-juice " sputum. Injected into rabbits, it produces death with very great certainty; and by passing the organism through these animals its virulence may be markedly increased. Like the influenza bacillus and even the diphtheria bacillus, this organism may be present in the mouth and lungs of perfectly healthy individuals, and it is only when the vitality of the system is lowered by cold or other depressing influences that pneumonia is induced; two factors, the presence of the bacillus and the, lowered vitality, being both necessary for the production of this disease in the human subject. It is quite possible, however, that, as in the case of cholera, a slight inflammatory exudation may supply a nutrient medium in which the bacillus rapidly acquires greatly increased virulence, and so becomes a much more active agent of infection. It is claimed by the brothers Klemperer, by Washbourn and by others, that they have been able to produce an anti-pneumococcic serum, by means of which they are able to treat successfully severe cases of pneumonia. The catarrhal pneumonia so frequently met with during the course of ,whooping-cough, measles and other specific infective fevers, is also in all probability due to the action of some organism of which the influenza bacillus and the Diplococcus pneumoniae are types. Infective meningitis is, in most of the recent works on medicine, divided into four forms: (1) the acute epidemic cerebro-spinal form; (2) a posterior basic form, which, however, is closely allied to the first; (3) suppurative meningitis, usually associated with pneumonia, erysipelas, and pyaemia; and (4) tubercular meningitis, due to the specific tubercle bacillus. 1. The first form, acute infective or epidemic cerebro-spinal meningitis, is usually associated with Weichselbaum's Diplococcus intracellularis meningitidis (two closely apposed disks), which is found in the exudate, especially in the leucocytes, of the meninges of the brain and cord. It grows, as transparent colonies, on blood-agar at the temperature of the body, but dies out very rapidly unless reinoculated, and has little pathogenetic effect on any of the lower animals, though under certain conditions it has been found to produce meningitis when injected under the dura mater. More or less successful attempts have been made to treat acute epidemic cerebro-spinal meningitis by means of antisera obtainedfrom different sources. Flexner uses the serum of horses that have been highly immunized against numerous strains of the meningo, coccus, the process of immunization extending over four or five months. Meister, Lucius and Bruning supply Ruppel's anti-bacterial serum derived from animals immunized against several strains of meningococcus of high pathogenic activity. Both these sera may be looked upon as polyvalent sera. Ivy Mackenzie and Martin, pointing out that the cerebro-spinal fluid, even of patients who have recovered from this form of meningitis, contains no anti-bodies, tried and recommended injections of the patient's own blood serum into the spinal canal. In all cases the action seems to be much the same. These sera contain immune body and complement, and are distinctly bactericidal, acting on the meningococcus and rendering it much more easily taken up and digested by the white blood corpuscles. It is possible that these sera may also exert some slight antitoxic action. The serum is injected directly into the spinal canal, a corresponding quantity of the cerebro-spinal fluid having first been withdrawn by lumbar puncture. The treatment thus resembles the treatment of lockjaw, where the antitetanus serum is brought as directly as possible into contact with the nerve centres. The dose of these sera ranges from 15 to 40 cc. according to the severity of the disease. Although the general mortality of the disease is from 50 to 80%, it is stated that where Flexner's serum is used the mortality falls to 33%. The result corresponds somewhat closely to those obtained with antidiphtheria serum in diphtheria. In patients injected on the first day of the disease the mortality was only about 15%, on and from the fourth to the seventh day 22 %, but after the seventh day 36 %. From this it is evident that although the serum has a distinct effect in bringing about the phagocytosis of the meningococcus and the neutralization of the toxins produced, it cannot make good any damage already done to the tissues. Mackenzie and Martin treated 20 cases with the blood taken from patients suffering, or convalescent, from meningitis. Of 16 acute cases treated 14 received serum from patients who had already recovered from the disease, 8 of the patients recovered, 6 died, and 2 cases which received their own serum both recovered. In the presence of these anti-cerebro-spinal-fever sera the meningeal cocci become diminished in number and do not stain so readily, whilst, simultaneously, the polymorpho-nuglear leucocytes seem to be diminished in number. The serum should be given until the temperature becomes normal. Mackenzie and Martin assert that even normal human blood contains substances which are bactericidal to the meningeal coccus, but that these substances increase " in amount and activity in the blood serum of patients suffering from an acute or chronic meningococcic infection, and the serum of a patient recently recovered from an infection shows the evidence of the presence of these substances in a still greater degree." They were able to demonstrate, moreover, that the destructive action on the cocci depends on an immune body which requires the presence of a complement to complete the process. The cerebro-spinal fluid differs from the serum in that it does not contain substances which kill this meningeal coccus in vitro, nor are the immune body and complement present in the blood, found in this cerebro-spinal fluid. Hence the efficacy of the blood when it is called upon to replace the fluid in the cerebro-spinal canal. 2. Posterior basic meningitis, according to Dr Still, "is frequently seen during the first six months of life, a period at which tuberculous and epidemic cerebro-spinal meningitis are quite uncommon." The organism found in this disease resembles the diplococcus intracellularis meningitidis very closely, but differs from it in that it remains alive without recultivation for a considerably longer period. It is less pathogenetic than that organism, of which possibly it is simply a more highly saprophytic form. This is a somewhat important point, as it would account for the great resemblance that exists between the sporadic and the epidemic forms of meningitis. 3. In suppurative meningitis these two organisms may still be found in a certain proportion of the cases, but their place may be taken by the pneumococcus or Diplococcus pneumoniae or Fraenkel's pneumococcus—Diplococcus lanceolatus—which appears to grow in two forms. In the first it is an encapsulated organism, consisting of small oval cocci arranged in pairs or in short chains; the capsule is unstained. When the pneumococcus grows in chains—the second form—as when cultivated outside the body, on blood-serum or on agar over the surface of which a small quantity of sterile blood has been smeared, it produces very minute translucent colonies. Like Weichselbaum's bacillus, it must be recultivated every three or four days, otherwise. it soon dies out. Unlike the other forms previously described, it may, when passed through animals, become extremely virulent, very small quantities being sufficient to kill a rabbit. Although the pneumococcus is found in the majority of these cases, especially in children, suppurative meningitis may also accompany or follow the various diseases that are set up by the Streptococcus pyogenes and Streptococcus erysipelatis; whilst along with it staphylococci and the Bacillus coil communis have sometimes been found. In other cases, again, there is a mixed infection of the pneumococcus and the Streptococcus pyogenes, especially in cases of disease of the middle ear. As might be expected in meningitis occurring in connexion with the specific infective diseases, e.g. influenza and typhoid fever, the presence of the specific bacilli of these diseases may usually be demonstrated in the meningeal pus or fluid. 4. The fourth form, tubercular meningitis (acute hydrocephalus), is met with most frequently in young children. It is now generally accepted that this condition is the result of the introduction of the tubercle bacillus into the blood-vessels and lymph spaces of the meninges at the base of the brain, and along the fissures of Sylvius. Influenza.—From 1889 up to the present time, influenza has every year with unfailing regularity broken out in epidemic form in some part of the United Kingdom, and often has swept over the whole country. The fact that the period of incubation is short, and that the infective agent is extremely active at a very early stage of the disease, renders it one of the most rapidly-spreading maladies with which we have to deal. The infective agent, first observed by Pfeiffer and Canon, is a minute bacillus or 'diplococcus less that rµ in length and o•5µ in thickness; it is found in little groups or in pairs. Each diplococcus is stained at the poles, a clear band remaining in the middle; in this respect it resembles the plague bacillus. It is found in the blood—though here it seems to be comparatively inactive—and in enormous numbers in the bronchial mucus. It is not easily stained in a solution of carbol-fuchsin, but in some cases such numbers are present that a cover-glass preparation may show practically no other organisms. Agar, smeared with blood, and inoculated, gives an almost pure cultivation of very minute transparent colonies, similar to those of the Diplococcus pneumoniae, but as a rule somewhat smaller. This organism, found only in cases of influenza, appears to have the power of forming toxins which continue to act for some time after recovery seems to have taken place; it appears to exert such a general devitalizing effect on the tissues that micro-organisms which ordinarily are held in check are allowed to run riot, with the result that catarrh, pneumonia and similar conditions are developed, especially when cold and other lowering conditions co-operate with the poison. This toxin produces special results in those organs which, through over-use, impaired nutrition or disease, are already only just able to carry on their work. Hence in cases of influenza the cause of death is usually associated with the failure of some organ that had already been working up to its full capacity, and in which the margin of reserve power had been reduced to a minimum. It is for this reason that rest, nutrition, warmth and tonics are such important and successful factors in the treatment of this condition. Yellow Fever, endemic in the West Indies and the north-eastern coast of South America, may become epidemic wherever the temperature and humidity are high, especially along the seashore in the tropical Atlantic coast of North America. It appears to be one of the specific infective fevers in which the liver, kidney, and gastro-intestinal systems, and especially their blood-vessels, are affected. In 1897 Sanarelli reported, in the Annales de l'Institut Pasteur, that he had found a bacillus in the blood-vessels of the liver and kidneys, and in the cells of the peritoneal fluid, but never in the alimentary tract, of yellow fever patients. These, he maintained, were perfectly distinct from the putrefactive microbes occurring in the tissues in the later stages, their colonies not growing like those of the bacillus coli communis. They grow readily on all the ordinary artificial nutrient media, as short rods with rounded ends, usually about 2 to 4µ in length and about half as broad as they are long. They are stained by Gram's method and readily by most of the aniline dyes, are ciliated, and do not liquefy gelatine. They flourish specially well alongside moulds, in the dark, in badly-ventilated, warm, moist places, and remain alive for some time in sea-water:these facts, as Sanarelli points out, may afford an explanation of the special persistence of yellow fever in old, badly-ventilated ships, and in dark, dirty and insanitary sea-coast towns. Once the organism, whatever it may be, finds its way into the system, it soon makes its presence felt, and toxic symptoms are developed. The temperature rises; the pulse, at first rapid, gradually slows down; and after some time persistent vomiting of bile comes, on. At the end of three or four days the temperature and pulse fall, and there is a period during which the patient appears comparatively well; this is followed in a few hours by icterus and scanty secretion of urine. There may be actual anuria, or the small quantity of urine passed may be loaded with casts and albumen; delirium, convulsions and haemorrhages from all the mucous surfaces may now occur, or secondary infections of various kinds, boils, abscesses, suppurations and septicaemia, may result. These often prove fatal when the patient appears to be almost convalescent from the original disease. As regards prognosis, it has been found that the " lower the initial temperature the milder will the case be " (Macpherson). An initial temperature of roe F. is an exceedingly unfavourable sign. Patients addicted to the use of alcohol are, as a rule, much more severely affected than are others. Treatment is principally directed towards. prevention and towards the alleviation of symptoms, though Sanarelli has hopes that an " anti "-serum may be useful. More recently S. Flexner, working with the . American Commission, isolated another organism, which, he maintains, is the pathogenetic agent in the production of yellow fever; whilst Durham and Myers maintain that a small bacillus previously observed• by G. M. Sternberg and others is the true cause of this disease. Professor Boyce, enumerating the hypotheses as to the cause of yellow fever, points out that as in the case of malaria, suspicion turned to " that form of Miasm which was supposed to arise from the mixture, in a marsh or on a mud flat, of salt with fresh water." It was early recognized that yellow fever was not carried directly from person to person, but little of definite character was known as to the poison and the method of its dissemination, and Fergusson states that " it is a terrestrial poison which high atmospheric heat generates amongst the newly arrived, and without that heat it cannot exist." The following passage from Beauperthuy (see his collected papers published in 1891) is quoted by Boyce: " But rubbish! the small amount of sulphuretted hydrogen or marsh gas which might arise from a marsh could not possibly hurt a fly, much less a man. It is not that, it is a mosquito called in Cumana the ` Zancudo bobo,' the striped or domestic mosquito." Beauperthuy, recently as he wrote, then stood almost alone in this opinion. Now we know that yellow fever, in common with other specific diseases, is caused by the action of an organized virus. The search for a vegetable parasite, bacillus or micro-coccus, as above indicated, has been very close and strenuous, but it may now be held that up to the present no bacillus or micrococcus, well authenticated as capable of causing yellow fever, has been discovered. Latterly a search has been made for protozoal organisms, organisms similar to those present in the blood of malarious patients and like conditions, or for spirochaetes similar to those associated with relapsing fever, and Boyce draws attention to the fact that a spirochaete has recently been identified in the tissues taken from cases of yellow fever. It has however been demonstrated that the virus, whatever it may be, is carried by a species of mosquito; this seems to favour the protozoan hypothesis, especially as it is found that the Stegomyia fasciata, Fab. (or S. calopus, Meig.), after taking the blood from an infected patient is not infective immediately but only becomes capable of infecting by its bite at the end of twelve days. It would appear therefore that residence in this mosquito is necessary for the material to become fully infective. During this period some special meta-morphosis may occur, and metamorphosis essential to the development of the parasite, or, on the other hand, the time may be required for it to make its way to some position from which it may emerge from the mosquito when that insect " strikes." In the interval between the bite of an infected Stegomyia and the appearance of the disease (5 or 6 days) the blood of the patient contains a virus which, when taken into the mosquito, may develop into the infective material; moreover, this virus persists alive and active for three days after the disease is fully developed, but at the end of this time it disappears, so far, at any rate, as its infective power is concerned, from the blood, secretions and tissues of the patient. Further, there is no evidence that the infective virus is ever transmitted directly from the patient in secretions or in fact in anything but blood or blood-serum. The infective material, then, is present in the human subject for about eight days, during which the blood and even the blood-serum may serve as a vehicle for the infective agent. If during this period the patient is bitten by the Stegomyia the mosquito cannot distribute the infection for twelve days, but after this the power of transmitting reinfection persists for weeks and even months during cold weather when the insect is torpid. As soon, however, as the warm weather comes round and the mosquito becomes active and again begins to bite there is evidence that it still maintains its power of transmitting infection; indeed Boyce states that mosquitos infected in one year are capable of transmitting infection and starting a fresh epidemic in the following warm season. When it is remembered that a mosquito by a single bite is capable of setting up an attack of the disease, we see how important is this question. The Stegomyia, known as the domestic or house mosquito, is spoken of as the " Tiger " mosquito, " Scots' Grey," or " Black and White Mosquito," from the fact that there is " a lyre-shaped pattern in white on the back of the thorax, transverse white bands on the abdomen, and white spots on the sides of the thorax; while the legs have white bands with the last hind tarsal joint also white " (Boyce). It is also spoken of as the " cistern mosquito," as it breeds in the cisterns, barrels, water butts, &c., containing the only water-supply of many houses. It may pass through its various stages of development in any small vessels, but the larvae are not usually found in natural collections of water, such as gutters, pools or wells, if the ovipositing insect can gain access to cleaner and purer water. The egg of the Stegomyia deposited on the water develops in from 10 to 20 hours into the larval form, the so-called " wiggle-waggle." It remains in this stage for from 1 to 8 days, then becomes a pupa, and within 48 hours becomes a fully developed mosquito. The larvae can only develop if they are left in water, though a very small amount of water will serve to keep them alive. The eggs on the other hand are very resistant, and even when removed from water may continue viable for as long a period as three months. The Stegomyia affects clean water-butts and cisterns by preference. Consequently its presence is not confined to unhygienic districts; they may, however, " seek refuge for breeding purposes in the shallow street drains and wells in the town." The Stegomyia does not announce its advent and attack by a " ping " such as that made by the Anopheles, it works perfectly noiselessly and almost ceaselessly (from 3 p.m. to early morning) so that any human beings in its neighbourhood are not safe from its attacks either afternoon or night. The most important prophylactic measures against the Stegomyia are ample mosquito nets " with a gauge of eighteen meshes to the inch " (Boyce), so arranged that the person sleeping may not come near the net; these nets should be used not only at night but at the afternoon siesta. Then the living room should be screened against the entrance of these pests, thorough ventilation should be secured; and all pools and stagnant waters, especially in the neighbourhood of houses, should be drained, water-butts and cisterns should be screened and all stagnant waters oiled with kerosene or petroleum, where drainage is impossible. What has been done through the carrying out of these and similar measures may be gathered from the record of the Panama Canal. In 1884 the French Panama Canal Company, employing from 15,000 to 18,000 men, lost by death6o per r000 annually (in r885 over 70 per 1000). In 1904, when the Americans had taken over the work of construction, Col. W. C. Gorgas undertook to clear the country of the Stegomyia, and within two or three years yellow fever had been eradicated. The death-rate from malaria was also greatly diminished, and by the end of 1907 the death-rate per annum amongst 45,000 workers was only 18 per 1000, a lower death-rate than is met with in many large English towns. Similar examples might be cited from other places, but the above is sufficiently striking to carry conviction that the methods employed in carrying on the warfare against tropical diseases have been attended with unexampled success. These diseases, at one time so greatly feared, are now so much under control that some one has said " ere long we shall be sending our patients to the tropics in search of a health resort." Weil's disease, a disease which may be considered along with acute yellow atrophy and yellow fever, is one in which there is an acute febrile condition, associated with jaundice, inflammation of the kidney and enlargement of the spleen. It appears to be a toxic condition of a less acute character, however, than the other two, in which the functions and structure of the liver and kidney are specially interfered with. There is a marked affection of the gastrointestinal system, and the nervous system is also in some cases profoundly involved. Haemorrhage into the mucous and serous membranes is a marked feature. The liver cells and kidney epithelium undergo fatty changes, though in the earlier stages there is a cloudy swelling, probably also toxic in origin. Organisms of the Proteus group, which appear to have the power, in certain circumstances, of forming toxic substances in larger quantities than can be readily destroyed by the liver, and which then make their appearance in the kidney and spleen, are supposed to be the cause of this condition. Diphtheria.—In regard to no disease has medical opinion under-gone greater modification than it has in respect of diphtheria. Accurately applied, bacteriology has here gained one of its greatest triumphs. Not only have the aetiology and diagnosis of this disease been made clear, but knowledge acquired in connexion with the production of the disease has been applied to a most successful method of treatment. In 1875 Klebs described a small bacillus with rounded ends, and with, here and there, small clear unstained spaces in its substance. He, however, also described streptococci as present in certain cases of diphtheria, and concluded that there must be two kinds of diphtheria, one associated with each of these organisms. In 1883 he again took up the question; and in the following year Loeffler gave a systematic description of what is now known as the Klebs-Loeffler bacillus, which was afterwards proved by Roux and Yersin and many other observers to be the causa causans of diphtheria. This bacillus is a slightly-curved rod with rounded, pointed, or club-shaped end or ends (see Plate IL fig 9). It is usually from 1.2 to 5µ or more in length and from o•3 to 0•5µ in breadth; rarely it may be considerably larger in both dimensions. It is non-motile, and may exhibit great variety of form, according to the age of the culture and the nature of the medium upon which it is growing. It is stained by Gram's method if the decolorizing process be not too pro-longed, and also by Loeffler's methylene-blue method. Except in the very young forms, it is readily recognizable by a series of transverse alternate stained and unstained bands. The bacillus may be wedge-shaped, spindle-shaped, comma-shaped or ovoid. In the shorter forms the polar staining is usually well marked; in the longer bacilli, the transverse striation. Very characteristic club-shaped forms or branching filaments are met with in old cultures, or where there is a superabundance of nutritive material. In what may be called the handle of the club the banded appearance is specially well marked. These specific bacilli are found in large numbers on the surface of the diphtheritic membrane (Plate II. fig. so), and may easily be detached for bacteriological examination. In certain cases they may be found by direct microscopic examination, especially when they are stained by Gram's method, but it is far more easy to demonstrate their presence by the culture method. On Loeffler's special medium the bacilli flourish so well at body-temperatureabout 370 C.—that, like the cholera bacillus, they outgrow the other organisms present, and may beobtained in comparatively pure culture. Distinct colonies may often be found as early as the eighth or twelfth hour of incubation; in from eighteen to twenty-four hours they appear as rounded, elevated, moderately translucent, greyish white colonies, with a yellow tinge, the surface moist and the margins slightly irregular or scalloped. They are thicker and somewhat more opaque in the centre. When the colonies are few and widely separated, each may grow to a considerable size, 4 to 5 mm.; but when more numerous and closer together, they remain small and almost invariably discrete, with distinct intervals between them. In older growths the central opacity becomes more marked and the crenation more distinct, the moist, shiny appearance being lost. When the surface of the serum is dry, the growth, as a rule, does not attain any very large size. These " pure " colonies, when sown in slightly alkaline broth, grow with great vigour; and if a small amount of such a 48 hours' culture be injected under the skin of a guinea-pig, the animal succumbs, with a marked local reaction and distinct symptoms of toxic poisoning very similar to those met with in cases of diphtheria of the human subject. Roux and Yersin demonstrated that the poison was not contained in the bodies of the bacilli, but that it was formed and thrown out by them from and into the nutrient medium. Moreover, they could produce all the toxic symptoms, the local reactions, and even the paralysis which often follows the disease in the human subject, by injecting the culture from which they had previously removed the whole of the diphtheria bacilli by filtration. This cultivation, then, contains a poisonous material, which; incapable of multiplying in the tissues, may be given in carefully graduated doses. If, therefore, there is anything in the theory that tissues may be gradually " acclimatized " to the poisons of these toxic substances, they saw that it should be possible to prove it in connexion with this disease. Behring, going still further, found that the tissues so acclimatized have the power of producing a substance capable of neutralizing the toxin, a substance which, at first confined to the cells, when formed in large quantities overflows into the fluids of the blood, with which it is distributed through-out the body. The bulk of this toxin-neutralizing substance remains in the blood-serum after separation of the clot. In proof of this he showed that (I) if this serum be injected into an animal before it is inoculated with even mere than a lethal dose of the diphtheria bacillus or its products, the animal remains perfectly well; (2) a certain quantity of this serum, mixed with diphtheria toxin and injected into a guinea-pig, gives rise to no ill effects; and (3) that even when injected some hours after the bacillus or its toxins, the serum is still capable of neutralizing the action of these substances. In these experiments we have the germ of the present antitoxic treatment which has so materially diminished the percentage mortality in diphtheria. This serum may also be used as a prophylactic agent. The antitoxic serum as now used is prepared by injecting into the subcutaneous tissues of a horse the products of the diphtheria bacillus. The bacillus, grown in broth containing peptone and blood-serum or blood-plasma, is filtered and heated to a temperature of 68° or 70° C. for one hour. It then contains only a small amount of active toxin, but injected into the horse it renders that animal highly insusceptible to the action of strong diphtheria toxins, and even induces the production of a considerable amount of antitoxin. This production of antitoxin, however, may be accelerated by subsequent repeated injections, with increasing doses of strong diphtheria toxin, which may be so powerful that c to a of a drop, or even less, is a fatal dose for a medium-sized guinea-pig. The anti-toxic serum so prepared may contain 200, 400, 600 or even more " units " of antitoxin per c.c.—the unit being that quantity of antitoxin that will so far neutralize too lethal doses (a lethal dose is the smallest quantity that will kill a 250-gramme guinea-pig on the fifth day) of toxin for a 250-gramme guinea-pig, that the animal continues alive on the fifth day from the injection. This, however, is a purely arbitrary stand ird of neutralizing power, as it is found that, owing to the complicated structure of the toxin, the neutralizing and the lethal powers do not always go hand in hand; but as the toxin used in testing the antitoxin is always compared with the original standard, accurate results are easily obtained. Diphtheria, though still prevalent in cities, has now lost many of its terrors. In the large hospitals under the Metropolitan Asylums Board the death-rate fell from nearly 40% in 1889 to under io% in 1903; and if antitoxin be given as soon as the disease manifests itself, the mortality is brought down to a very insignificant figure. It has been maintained that as soon as antitoxin came into use the number of cases of paralysis increased rather than diminished. This may be readily understood when it is borne in mind that many patients recover under the use of antitoxin who would undoubtedly have succumbed in the pre-antitoxin days; and it cannot be too strongly insisted that although the antitoxin introduced neutralizes the free toxin and prevents its further action on the tissues, it cannot entirely neutralize that which is already acting on the cells, nor can it make good damage already done before it is injected. Even allowing that antitoxin is not accountable for the whole of the improvement in the percentage mortality statistics since 1896, it has undoubtedly accounted for a very large proportion of recoveries. Antitoxin often cuts short functional albuminuria, but it cannot repair damage already done to the renal epithelium before the antitoxin was given. The clinical evidence of the value of antitoxin in the relief that it affords to the patient is even more important than that derived from the consideration of statistics. The diphtheria bacillus or its poison acts locally as a caustic and irritant, and generally or constitutionally as a protoplasmic poison, the most evident lesions produced by it being degeneration of nerves and muscles, and, in acute cases, changes in the walls of the blood-vessels. Other organisms, streptococci or staphylococci, when present, may undoubtedly increase the mortality by producing secondary complications, which end in suppuration. Diphtheria bacilli may also be found in pus, as in the discharges from cases of otorrhoea. Tetanus (Lockjaw): Although tetanus was one of the later diseases to which a definite micro-organismal origin could be assigned, it has long been looked upon as a disease typical of the "septic" group. In 1885 Nicolaier described an organism multiplying outside the body and capable of setting up tetanus, but this was only obtained in pure culture by Kitasato, a Japanese, and by the Italians in 1889. It has a very characteristic series of appearances at different stages of its development. First it grows as long, very slender threads, which rapidly break up into shorter sections from 4 to 5 µ in length (see Plate II. fig. 11). In these shorter rods spores may appear on the second or up to the seventh day, according to the temperature at which the growth occurs. The rods then assume a very characteristic pin or drumstick form; they are non-motile, are somewhat rounded at the ends, and at one end the spore, which is of greater diameter than the rod, causes a very considerable expansion. Before sporulation the organisms are distinctly motile, occurring in rods of different lengths, in most cases surrounded by bundles of beautiful flagella, which at a later stage are thrown off, the presence of flagella corresponding very closely with the " motile " period. The bacillus grows best at the temperature of the body; it becomes inactive at 14° C. at the one extreme, and at from 42° to 43° C. at the other; in the latter case involution forms, clubs and branching and degenerated forms, often make their appearance. It is killed by exposure for an hour to a temperature of from 6o° to 65° C.; the spores however are very resistant to the action of heat, as they withstand the temperature of boiling water for several minutes. The organism has been found in garden earth, in the excrement of animals—horses—and in dust taken from the streets or from living-rooms, especially when it has been allowed to remain at rest for a considerable period. It has also been demonstrated in, and separated from the pus of wounds (see Plate II. fig. 12) in patients suffering from lockjaw, though it is then invariably found associated with the micro-organisms that give rise to suppuration. It is important to remember that this bacillus is a strict anaerobe, and can only grow when free oxygen has been removed from the cultivation medium. It may be cultivated in gelatine to which has been added from 2 to 3 % of grape-sugar, when, along the line of the stab culture, it forms a delicate growth, almost like a fir-tree, the tip of which never comes quite to the surface of the gelatine. The most luxuriant growth—evidenced by the longest branches—occurs in the depth of the gelatine away from free oxygen. After a time the gelatine becomes sticky, and then undergoes slow liquefaction, the growth sinking and leaving the upper layers comparatively clear. This organism is not an obligate parasite, but a facultative; it may grow outside the body and remain alive for long periods. Lockjaw is most common amongst agricultural labourers, gardeners, soldiers on campaign, in those who go about with bare feet, or who, like young children, are liable to get their knees or hands accidentally wounded by rough contact with the ground. Anything which devitalizes the tissues—such as cold, bruising, malnutrition, the action of other organisms and their products—may all be predisposing factors, in so far as they place the tissue at a disadvantage and allow of the multiplication and development of the specific bacillus of tetanus. In order to produce the disease, it is not sufficient merely to inoculate tetanus bacilli, especially where resistant animals are concerned: they must be injected along with some of their toxins or with other organisms, the presence of which seems to increase the power of, or assist, the tetanus organism, by diverting the activity of the cells and so allowing the bacillus to develop. The poison formed by this organism resembles the enzymes and diphtheria poison, in that it is destroyed at a temperature of 65° C. in about five minutes, and even at the temperature of the body soon loses its strength, although, when kept on ice and protected from the action of light, it retains its specific properties for months. Though slowly formed, it is tremendously potent, areas a part of a drop (the five-millionth part of a c.c.) of the broth in which an active culture has been allowed to grow for three weeks or a month being sufficient to kill a mouse in twenty-four hours, cgs of a drop killing a rabbit, is a dog, or s Is of a drop a fowl or a pigeon; it is from too to 400 times as active as strychnine, and 400 times as poisonous as atropine. It has been observed that, quite apart from size, animals exhibit different degrees of susceptibility. Frogs kept at their ordinary temperature are exceedingly insusceptible, but when they are kept warm it is possible to tetanize them, though only after a somewhat prolonged incubation period, such as is met with in very chronic cases of tetanus in the human subject. In experimentally-produced tetanus the spasms usually commence and are most pronounced in the muscles near the site of inoculation. It was at one time supposed that this was because the poison acted directly upon the nerve terminations, or possibly upon the muscles; but as it is now known that it acts directly on the cells of the central nervous system, it may, as in the case of rabies, find its way along the lymphatic channels of the nerves to those points of the central nervous system with which these nerves are directly connected, spasms occurring in the course of the muscular distribution of the nerves that receive their impulses from the cells of that area. As the amount of toxin introduced may be contained in a very small quantity of fluid and still be very dilute, the local reaction of the connective-tissue cells may be exceedingly slight; consequently a very small wound may allow of the introduction of a strong poisonous dose. Many of the cases of so-called idiopathic tetanus are only idiopathic because the wound is trifling in character, and, unless suppuration has taken place, has healed rapidly after .the poison has been introduced. In tetanus, as in diphtheria, the organisms producing the poison, if found in the body at all, are developed only at the seat of inoculation; they do not make their way into the surrounding tissues. In this we have an explanation of the fact that all the earlier experiments with the blood from tetanus patients gave absolutely negative results. It is sometimes stated that the production of tetanus toxin in a wound soon ceases, owing to the arrest of the development of the bacillus, even in cases that ultimately succumb to the disease. Roux and Vaillard, however, maintain that no case of tetanus can be treated with any prospect of success unless the focus into which the bacilli have been introduced is freely removed. The antitetanus serum was the first antitoxic serum produced. It is found, however, that though the antitetanic serum is capable of acting as a prophylactic, and of preventing the appearance of tetanic symptoms in animals that are afterwards, or simultaneously, injected with tetanus toxin,it does not give very satisfactory results when it is injected after tetanic symptoms have made their appearance. It would appear that in such cases the tetanus poison has become too firmly bound up with the protoplasm of the nerve cells, and has already done a considerable amount of damage. (b) More Chronic Infective Diseases (Tissue Parasites). Tuberculosis.—In no quarter of the field of preventive medicine have more important results accrued from the discovery of a specific infective organism than in the case of Koch's demonstration and separation in pure culture of the tubercle bacillus and the association of this bacillus with the transmission of tuberculosis. In connexion with diagnosis—both directly from observation of the organism in the sputum and urine of tuberculous patients, and indirectly through the tuberculin test, especially on animals—this discovery has been of very great importance; and through a study of the life-history of the bacillus and its relation to animal tissues much has been learned as to the prevention of tuberculosis, and something even as to methods of treatment. One of the great difficulties met with in the earlier periods of the stud}- of this organism was its slow, though persistent, growth. At first cultivations in fluid media were not kept sufficiently long under observation to allow of its growth; it was exceedingly difficult to obtain pure cultures, and then to keep them, and in impure cultures the tubercle bacilli were rapidly overgrown. Taken directly from the body, they do not grow on most of the ordinary media, and it was only when Koch used solidified blood-serum that he succeeded in obtaining pure cultures. Though they may now be demonstrated by what appear to be very simple methods, before these methods were devised it was practically impossible to obtain any satisfactory results. The principle involved in the staining of the tubercle bacillus is that when once it has taken up fuchsin, or gentian violet, it retains the stain much more firmly than do most organisms and tissues, so that if a specimen be thoroughly stained with fuchsin and then decolorized by a mineral acid—25 % of sulphuric acid, say—although the colour is washed out of the tissues and most other organisms, the tubercle bacilli retain it; and even after the section has beeh stained with methylene-blue, to bring the other tissues and organisms into view, these bacilli still remain bright red, and stand out prominently on a blue background. If a small fragment of tuberculous tissue be pounded in a sterile mortar and smeared over the surface of inspissated blood-serum solidified at a comparatively low temperature, and if evaporation be prevented, dry scaly growths make their appearance at the end of some fourteen days. If these be reinoculated through several generations, they ultimately assume a more saprophytic character, and will grow in broth containing 5% of glycerin, or on a peptone beef-agar to which a similar quantity of glycerin has been added. On these media the tubercle bacillus grows more luxuriantly, though after a time its virulence appears to be diminished. On blood-serum its virulence is preserved for long periods if successive cultivations be made. It occurs in the tissues or in cultivations as a delicate rod or thread 1'5 to 3.5µ in length and about o.2 to 0.5µ in thickness (see Plate II., fig. 15). It is usually slightly curved, and two rods may be arranged end to end at an open angle. There is some doubt as to whether tubercle bacilli contain spores, but little masses of deeply-stained protoplasm can be seen, alternating with clear spaces within the sheath; these clear spaces have been held to be spores. This organism is found in the lungs and sputum in various forms of consumption; it is met with in tuberculous ulcers of the intestine, in the lymph spaces around the vessels in tuberculous meningitis, in tuberculous nodules in all parts of the body, and in tuberculous disease of the skin—lupus. It is found also in the tuberculous lesions of animals; in the throat-glands, tonsils, spleen and bones of the pig; in the spleen of the horse; and in the lungs and pleura of the cow. Tuberculosis may be produced artificially by injecting the tubercle bacillus into animals, some being much more susceptible than others. Milk drawn from an udder in which there are breaking-down tuberculous foci, may contain an enormous number of active tubercle bacilli; and pigs fed upon this milk develop a typical tuberculosis, commencing in the glands of the throat, which can be traced from point to point, with the utmost precision. It must be assumed that what takes place in the pig may also take place in the human subject; and a sufficient number of cases are now on record to show that the swallowing of tuberculous material is a cause of tuberculosis, especially amongst children and adolescents. Inhaled tubercle bacilli from the recently-dried sputum of phthisical patients, like milk derived from tuberculous udders, may set up tuberculosis of the lungs or of the alimentary tract, especially when the epithelial layer is unhealthy or imperfect. The two main causes of the prevalence of tuberculosis in the human subject are: (I) tubercle bacilli may become so modified that they can flourish saprophytically; as yet it has not been possible to trace the exact conditions under which they live, but we are gradually coming to recognize that, although when they come from the body they are almost obligate parasites, they may gradually acquire saprophytic characters. (2) Many of the domestic animals are readily infected with tuberculosis, and in turn may become additional centres from which infection may radiate. Koch's tuberculin has been of inestimable value in the early diagnosis of tuberculosis, especially in animals. Tuberculin, from which the tuberculin test derives its name, consists of the products of the tubercle bacillus when grown for a month or six weeks in peptone meat-broth to which a small proportion, say 5 or 6%, of glycerin has been added. The tubercle bacilli are then killed at boiling-temperature, and are partially removed by sedimentation, and completely by filtration through a Berkfeld or Pasteur-Chamberland filter. If a large dose of this filtered fluid be injected under the skin of a healthy man or brute, it is possible to produce some local swelling and to induce a rise of temperature; but in a similar patient suffering from tuberculosis a very much smaller dose (one which does not affect the healthy individual in the slightest degree) is sufficient to bring about the characteristic swelling and rise of temperature. To obtain trustworthy results the dosage must always be carefully attended to. The reaction is only obtained under certain well-defined conditions. Driven animals seldom, if ever, react properly. Cattle to be tested should be allowed to remain at rest for some time; they should be well fed, and be carefully protected from cold or draughts. After an injection of tuberculin into the subcutaneous tissues (usually in front of the shoulder or on the chest-wall) they should be kept under the same conditions and should be watched very carefully; the temperature should be taken at the sixth hour, and every three hours afterwards up to the twenty-first or even twenty-fourth hour. If during this time the temperature rises to 104° F., there can be little doubt that the animal is tuberculous; but if it remains under 103° the animal must be considered free from disease: if the temperature remains between these points the case is a doubtful one, and, according to Sir John M'Fadyean, should be retested at the end of a month. It is interesting to note that the test is not trustworthy in the case of animals in which tuberculosis is far advanced, especially when the temperature is already high—1o3° F. In such cases, however, it is an easy matter to diagnose the disease by the ordinary clinical methods. At first objections were raised to this test on two grounds: (i) that mistakes in diagnosis are sometimes made; (2) that tuberculin may affect the milk of healthy animals into which it is injected. As the methods of using the tuberculin have been perfected, and as the conditions under which the reaction is obtained have become better known, mistakes have rapidly become fewer; whilst it has been amply proved that tuberculin has not the slightest deteriorating effect on the quality of the milk. Tuberculin and similar substances are sometimes used as specific reagents in the diagnosis of tuberculosis in the human subject. When small quantities of old tuberculin are injected subcutaneously into a tuberculous patient in whom, however, no tubercle bacilli may be. demonstrable, the temperature begins to rise in six or eight hours and continues to rise for twelve hours or, in rare cases, for an even longer period, a rise of a single degree being considered sufficient to indicate the presenee of the disease. Along with this there is usually some swelling and tenderness, with perhaps redness at the seat of injection, whilst there is also some evidence of a vascular congestion in the neighbourhood of any tuberculous lesion. A second method of applying tuberculin as a diagnostic reagent is that of Pirquet, who, after diluting old tuberculin with two parts of normal saline solution and one part of 5% carbolic glycerin, places a drop of the mixture on the skin and scrapes away the epidermis in lines with " a small dental burr." The skin is similarly treated with normal saline some 2 or 3 in. away from that at which the tuberculin is used. In the tuberculin area a little papule develops; this may become a vesicle, surrounded by slight redness and swelling (in the " saline " area nothing of the kind appears). The swelling begins about six hours after the scarification is made and continues to increase for24 hours. Reactions, however, are obtained by this test in patients who are not suffering from any active tubercular lesion, whilst on the other hand in certain cases it fails to indicate the presence of tubercle when it is undoubtedly there. Calmette's or Wolff-Eisner's ophthalmic reaction test, a third method of using tuberculin, consists in dropping a weak solution of tuberculin into the conjunctival sac of one eye; this is followed by a mild attack of conjunctivitis or inflammation of the eye in the tuberculous patient, whilst in the normal patient no such inflammation should appear. Although this test appears to be of considerable value, it fails to give any information in cases of advanced tuberculosis, of general miliary tuberculosis and of tuberculous meningitis. It certainly possesses one great advantage over the others—it does not give any reaction in the presence of dormant tubercle in persons clinically sound and healthy. The inflammation of the eye may, however, be so acute, especially where strong solutions of tuberculin are used, that considerable damage may be done, more especially should there be any dormant disease of the eye. It must be remembered that in all these tests the exhibition of tuberculin increases for a time the sensitiveness of the patient each time it is administered. It sets up a negative phase, as already described, and renders the patient more susceptible to the action of a fresh dose. It is evident, therefore, that the careful worker wishing to obtain minimal effects will give small doses and gradually repeat these as he may find necessary. In 1890 Koch, whose brilliant researches on tuberculosis had opened up a new field of investigation and had inspired new hope in the breasts of patients and physicians alike, followed up his method of diagnosis with a method of vaccination with the products of the tubercle bacillus separated from glycerinated broth culture after the vitality of the bacilli had been destroyed. As is frequently the case with new remedies, this was used so indiscriminately that it soon fell into disrepute. The results in certain cases, however, were so successful that careful investigations into the character and action of tuberculin and into the conditions under which it may be used with advantage were undertaken. Tuberculins composed of the triturated bodies of tubercle bacilli, of the external secretions of these bacilli, and of their various constituents in different combinations, were experimented with, but at the present time Koch's two tuberculinsespecially his new tuberculin---hold the field. The " old tuberculin " consists of the glycerin broth culture of the tubercle bacilli mentioned above. The new tuberculin consists of the centrifugalized deposit from a saline solution of the extract of the triturated dead tubercle bacilli; this is stored in small tubes, each containing two milligrammes of solid substance. This is diluted with distilled water containing 20% of glycerin, great care being taken to maintain the sterility of the solution. The dose is usually from - - to T (F of a milligramme for an adult, increasing toy; according to Sir A. Wright it should not go beyond this. Perhaps no one has done more to rehabilitate the tuberculin treatment than Sir Almroth Wright, who after a long series of experiments devised what he called the tuberculo-opsonic index, about which a few words may be of interest. It is well-known that certain cells in the human blood have the power of taking bacteria into their substance and there digesting them. This, the so-called " phagocytic power " of Metchnikoff, was found to vary somewhat under different conditions, and Wright set himself to determine, if possible, what were the factors that modified this variability. He found that the white blood corpuscles, the polymorphonuclear cells, whether from healthy or tuberculous patients, always showed practically the same phagocytic activity when mixed with a fine emulsion of tubercle bacilli and the serum from a healthy patient. If, however, corpuscles from the same individuals, whether healthy or tuberculous, were allowed to act upon the bacilli in the presence of serum drawn from a tuberculous patient, one of three things might happen: (i) the bacilli might be taken up in smaller numbers than in the above series of experiments; (2) they might be taken up in larger numbers; or (3) they might be taken up in what might be called normal numbers. In (i) and (2) Wright holds there is evidence of a tuberculous condition, in (3) of course the evidence is negative. He found, however, that when a dose of tuberculin was injected into a tuberculous patient there was a distinct fall in the number of tubercle bacilli taken up by the leucocytes treated with the serum of the patient. This condition Wright speaks of as the " negative phase. ' Increased phagocytic activity of the cells is associated with what is spoken of as the positive phase. The theory is that the blood serum has the power of preparing bacteria to be eaten by the phagocytes in the same sense that boiling, say, prepares food for ready digestion by the human subject, and Wright applied the term opsonin to the unknown constituent or complex of constituents of the serum that exerts this action upon the bacteria. The opsonic index is obtained by comparing the average number of bacilli taken up by, say, ioo leucocytes,, to which the serum from a tuberculous patient has been added, with the number of bacteria taken up by alhundred similar corpuscles to which normal serum has been added, the ratio between the two giving the opsonic index. Wright main- ' tains that after the injection of small doses of tuberculin during a negative phase which first appears, i.e. whilst there is a fall in the number of bacilli taken up by the leucocytes of the blood, the patient is more susceptible than before to the attacks of the tubercle bacillus. Following this, however, there is a gradual rise in the opsonic index until it passes the normal and the patient enters a positive phase, during which the susceptibility to the attacks of the tubercle bacillus is considerably diminished. When the effects of this dose are passing off a fresh injection should be made; this again induces a negative phase, but one that should not be so marked as in the first instance, whilst the positive phase which succeeds should be still more marked than that first obtained. If this can be repeated systematically and regularly the patient should begin, and continue, to improve. The difficulties involved in the determination of the opsonic index are, however, exceedingly great, and the personal factor enters so largely into the question that some observers are very doubtful as to the practical utility of this method. In Wright's hands, however, and in the hands of those who work with him, very satisfactory results are obtained. The tuberculin treatment, fortunately, does not stand or fall by the success of the opsonic index determination, especially as most valuable information as to the course of the disease and the effects of the tuberculin may be obtained by a study of the daily temperature chart and of the general condition of the patient. Tuberculin should not be injected more frequently than, about once in to or 14 days, and it is well not to increase the dose too rapidly. Wherever the temperature continues high, even a degree beyond normal, and where the pulse is over too, it is not wise to give tuberculin, nor does it seem to be of any great value where the disease is making rapid headway or has become generalized, especially where there is meningitis or bleeding from the lungs. It is interesting to note, in connexion with the diagnostic significance of the opsonic index, that in non-tuberculous subjects the administration of a small dose of tuberculin is followed by no negative phase such as is met with in the tuberculous subject. The phagocytic power of the white blood corpuscles is determined by noting the number of organisms taken up by the leucocytes when mixed with equal parts of a standard emulsion of tubercle bacilli and blood serum incubated in fine glass tubes for 15 minutes at a temperature of 37° C. If the period of incubation is much shorter than this the results are irregular, whilst if the period is.longer so many organisms are taken up that it becomes impossible to differentiate two sets of sera. As an example we might adduce the following. Taking a tubercu= lous patient's serum + leucocytes + tubercle bacilli, let us say we have an average of i•8 bacilli per leucocyte in 5o or 100 leucocytes counted; with normal serum + corpuscles + tubercle bacilli the average number of bacilli per leucocyte in the same number of cells counted is 3. From these figures the opsonic index obtained is 1.8 a 3 = o•6 = opsonic index. Leprosy.—Armauer Hansen in 1871, and Neisser in 1881, described a " leprosy bacillus " corresponding in size and in certain points of staining reaction to the tubercle bacillus, and it is now generally accepted that this bacillus is the direct and specific causal agent of leprosy. The discovery of this organism paved the way for the proof that the tubercular and anaesthetic forms of leprosy are essentially the same disease, or rather are the manifestations of the action of a common organism attacking different series of tissues. To demonstrate the presence of the leprosy bacillus, tie an indiarubber ring firmly around the base of one of the leprosy tubercles. As soon as the blood is driven out, leaving the nodule pale, make a puncture with the point of a sharp knife. From this puncture a clear fluid exudes; this, dried on a cover-glass, stained with carbol-fuchsin, and rapidly decolorized with a weak mineral acid, shows bacilli stained red and very like tubercle bacilli; they differ from that organism, however, in that they are somewhat shorter, and that if the acid be too strong or be allowed to act on them for too long a time, the colour is discharged from them much more readily. These organisms, which are from 4 to 6µ in length and 0•3µ in breadth, are as a rule more rigid and more pointed than are the tubercle bacilli (see Plate II., fig. 16). It is doubtful whether they form spores. They are found in large numbers lying embedded in a kind of gelatinous substance in the lymphatics of the skin, in certain cells of which they appear to be taken up. It is curious that these bacilli affect specially the skin and nerves, but rarely the lungs and serous membranes, thus being in sharp contrast to the tubercle bacillus, which affects the latter very frequently and the former more rarely. They are seldom found in the blood, though they have been described as occuring there in the later stages of the disease. It is stated that leprosy has been inoculated directly into the human subject, the patient dying some five or six years after inoculation; but up to the pre-sent no pure culture of the leprosy bacillus has been obtained; it has therefore been impossible to produce the disease by the inoculation of the bacillus only. What evidence we have at our disposal, however, is all in favour of the transmissibility of the disease from patient to patient and through the agency of the leprosy bacillus. None of the numerous non-bacillary theories of leprosy account at all satisfactorily for this transmissibility of the disease, for its progressive nature, and for the peculiar series of histological changes that are met with in various parts and organs of the leprous body. Leprosy occurs in all climates. It is found where no fish diet can be obtained, and where pork and rice are never used, though to these substances has been assigned the power of giving rise to the disease. Locality appears to influence it but little, and with improved sanitation and increased cleanliness it is being gradually eradicated. The only factor that is common in all forms of leprosy, and is met with in every case, is the specific bacillus; and in spite of the fact that it has yet been found impossible to trace the method of transmission, we must from what is known of the presence and action of bacilli, in other diseases, especially in tuberculosis, assign to the leprosy bacillus the r6le of leprosy-producer, until much stronger evidence than has yet been obtained can be brought forward in favour of any of the numerous other causes that have been assigned. Two cases are recorded in which people have contracted leprosy from pricking their fingers with needles whilst sewing a leper's clothes; and a man who had never been out of Dublin is said to have contracted the disease by sleeping with his brother, a soldier who had returned from India suffering from leprosy. Glanders.—Farcy in the human subject resembles the same disease experimentally produced in animals with material from a glandered animal, and as there is no pathological distinction between the two, from the aetiological standpoint, they may be considered together. If the pus from a glanders abscess be mixed with a little sterile saline solution and spread over the cut surface of a boiled potato kept at the body-temperature, bright yellow or honey-coloured, thick, moist-looking colonies grow very rapidly and luxuriantly. These colonies gradually become darker in colour, until they assume a cafe-au-lait, or even a chocolate, tint. On examining one of them microscopically, it is found to be made up of bacilli 2 to 5µ long and -- to - of their own length broad (see Plate I., fig. 2 and fig. 6). The bacillus is usually straight or slightly curved and rounded at one end; it appears to be non-motile. As first pointed out by Loeffler and Schutz, when a portion of a culture is inoculated subcutaneously, typical farcy, with the acute septicaemia or blood-poisoning so characteristic of certain cases of glanders and farcy, is the result. The human subject is usually inoculated through wounds or scratches, or through the application of the nasal discharge of a glandered animal to the mucous membrane of the nose or mouth. Man is not specially susceptible to the glanders virus, but as he frequently comes into contact with glandered horses a consider-able number of cases of farcy in man are met with, although amongst knackers it is a comparatively rare disease. Cattle never contract it by the ordinary channels, and even when inoculated exhibit nothing more than localized ulceration. The goat appears to occupy an intermediate position between cattle and the horse in this respect; in sheep, which are fairly susceptible the disease runs its course slowly, and appears to resemble chronic farcy in man. In rabbits and the dog the disease runs a very slow and modified course. Although field-mice are extra-ordinarily susceptible, white mice and house mice, unless previously fed on sugar or with phloridzin, are unaffected by inoculation of the glanders bacillus. The pigeon is the only bird in which glanders has been produced. Lions and tigers are said to contract the disease, and to take it in a very severe and rapidly fatal form. The glanders organism soon loses its virulence and even its vitality. Dry, it dies in about ten days; placed in distilled water, in about five days; but kept moist, or on culture media, it retains its vitality for about a month, although its activity soon becomes considerably lessened. These bacilli are readily killed at a temperature of 550 C.; they can pass through the kidneys, even when there is no lesion to be made out either with the naked eye or under the microscope (Sherrington and Bonome). The glanders bacillus grows best in the presence of oxygen, but it may grow anaerobically; it then appears to have the power of forming toxin, either more in quantity or of greater activity than when it has access to a free supply of oxygen. This poison (mallein) is used for the purpose of diagnosing the presence of glanders. A cultivation is made in peptonized bouillon to which a small portion of glycerin has been added. The bacillus is allowed to grow and multiply at the temperature of the body for a month or six weeks; the organisms are then killed by heat and 0.5% carbolic acid is added. The cultivation is then filtered through a porcelain filter in order to remove the bodies of the bacilli, and the resulting fluid, clear and amber-coloured, should have the power, when injected in quantities of r c.c., of giving the specific reaction in an animal suffering from glanders; in a healthy animal 6 c.c. will give no reaction. The suspected animal should be kept at rest and in a warm stable for twenty-four to forty-eight hours before the test is applied. The temperature should be normal, as no proper reaction is obtained in an animal in which the temperature is high. This reaction, which is a very definite one, consists in a rise of temperature of from 2° to 4° F., and the appearance of a swelling of from 3 to 4 in. in diameter and from r to ra in. in height, before the sixteenth or eighteenth hour; this swelling should continue to increase for some hours It has been suggested that the injection of - S to ilg c.c. of mallein, at intervals of two or three days, may be used with advantage in the treatment of glanders. Glandered horses seem to improve under this treatment, and then certainly do not react even to much larger doses of mallein. The mallein test has revealed the fact that glanders is a far more common and more widespread disease than was at one time supposed. II.—To HIGHER VEGETABLE PARASITES Actinomycosis.—This disease is very prevalent in certain low-lying districts, especially amongst cattle, giving rise to the condition known as " sarcoma," " wooden tongue," " wens," " bony growths on the jaw," &c. It is characterized by the presence of a fungus, which, at first growing in the form of long slender threads that may be broken up into short rods and cocci, ultimately, as the result of a degenerative process, assumes the form of a " ray-fungus," in which a series of club-like rays are arranged around a common centre (see Plate I., fig. 8). It is probably a streptothrix—Streptothrix Forsleri. Numerous cases have been observed in the human subject. Suppuration and the formation of fistulous openings, surrounded by exuberant granulations, " proud flesh," usually supervene where it is growing and multiplying in the tissues of the human body, and in the pus discharged are yellowish green or reddish brown points, each made up of a central irregular mycelium composed of short rods and spores, along with the clubs already mentioned. The mycelial threads may reach a considerable length (2o to cooµ); some of them become thicker, and are thus differentiated from the rest; the peripheral club is the result of swelling of the sheath; the filaments nearer the centre of the mycelial mass contain spores, which measure from r to 2µ in diameter. This fungus appears to lead a saprophytic existence, but it has the power of living in the tissues of the animal body, to which it makes its way through or around carious or loose teeth, or through abrasions of the tongue or tonsils. After the above positions, the abdomen, especially near the vermiform appendix, is a special seat of election, or in some cases the thorax, the lesions being traceable downwards from the neck. Any of the abdominal or thoracic organs may thus be affected. The process spreads somewhat slowly, but once started may extend in any direction,its track being marked by the formation of a large quantity of fibrous tissue, often around a long fistula. In the more recent growths, and in solid organs, cavities of some size, containing a soft semi-purulent cheesy-looking material, may be found, this mass in some cases being surrounded by dense fibrous tissue. When once a sinus is formed the diagnosis is easy, but before this the disease, where tumours of considerable size are rapidly formed, may readily be mistaken for sarcoma, or when ' the lungs are affected, for tuberculosis, especially as bronchitis and pleuritic effusion are frequently associated with both actinomycosis and tuberculosis. Mycetoma, the Madura foot of India, is a disease very similar to actinomycosis, and, like that disease, is produced by a some-what characteristic streptothrix. It usually attacks the feet and legs, however, and appears to be the result of infection through injured tissues. Under certain conditions and in long-standing cases the fungus appears to become pigmented (black) and degenerated. Other forms of fungus disease or Mycoses are described. Aspergillosis, or pigeon-breeders' disease, is the result of infection with the Aspergillus fumigatus. Certain tumours appear to be the result of the action of a yeast, Blastomycosis or Saccharomycosis. The spores of the Pencillium glaucum, and of some of the Mucors, are also said to have the power of setting up irritation, which may end in the formation of a so-called granuloma or granulation tissue tumour. These, however, are comparatively rare. B.—Diseases due to Animal Parasites. I.—To PROTOZOA Malaria.—Following Laveran's discovery, in 188o, of a parasite in the blood of patients suffering from malaria, our knowledge of this and similar diseases has increased by leaps and bounds, and most important questions concerning tropical diseases have now been cleared up. Numerous observations have been carried out with the object of determining the parasitic forms found in different forms of malaria—the tertian, quartan, and aestivo-autumnal fever—in each of which, in the red blood corpuscles, a series of developmental stages of the parasite from a small pale translucent amoebiform body may be followed. This small body first becomes lobulated, nucleated and pigmented; it then, after assuming a more or less marked rosette-shape ,with a deeply pigmented centre, breaks up into a series of small, rounded, hyaline masses of protoplasm, each of which has a central bright point. The number of these, contained in a kind of capsule, varies from 8 to ro in the quartan, and from r 2 to 20 in the tertian and aestivo-autumnal forms. There are certain differences in the arrangement of the pigment, which is present in larger quantities and distributed over a wider area in the somewhat larger parasites that are found in the tertian and quartan fevers. In the parasite of the aestivo-autumnal fever the pigment is usually found in minute dots, dividing near the pole at the point of division of the organism, along with it in the earlier stages (see Plate I., fig. 5). Here, too, the rosette form is not so distinct as in the parasite of tertian fever, and in the latter is not so distinct as in the quartan parasites. These dividing forms make their appearance immediately before the onset of a malarial paroxysm, and their presence is diagnostic. The process of division goes on especially in the blood-forming organs, and is therefore met with more frequently in the spleen and in bone-marrow than in any other situation. The parasites, at certain stages of their development, may escape from the red blood corpuscles, in which case (especially when exposed to the air for a few minutes) they send out long processes of protoplasm and become very active, moving about in the plasma and between the corpuscles, sometimes losing their processes, which, however, continue in active movement. In the aestivo-autumnal fever curious crescent-shaped or ovoid bodies were amongst the first of the parasitic organisms described as occurring in the blood, in the red corpuscles of which they develop. Manson maintains that from these arise the flagellate forms, all of which, he thinks, are developed in order that the life of the malarial parasite may be continued outside the human body. It is probable that most of the pigment found in the organs taken from malarial patients is derived from red blood corpuscles broken down by the malarial parasites; many of these, in turn, are devoured by leucocytes, which in malarial blood are usually greatly increased in number, and frequently contain much pigment, which they have obtained either directly from the fluid plasma or from the pigmented parasitic organism. The work recently carried out by Bruce on the tsetse-fly parasite, by A. J. Smith on Texas fever, and by W. S. Thayer and Hewitson on the blood parasites of birds, has opened up the way for the further study of the malarial parasites outside the human body. There can be no doubt as to the close relation of the multiplication and sporulation of the malarial parasite with the ague paroxysm: the anaemia results from the breaking down of blood corpuscles. Toxic substances are present in the blood during the setting free of the spores; of this we have proof in the increased toxicity of the urine during the paroxysmal stages of the disease; more-over necrotic areas, similar to those found in acute toxic fevers produced by other micro-organisms, are met with. It is well to bear in mind that the accumulation of debris of parasites and corpuscles in the capillaries may be an additional factor in this necrosis, especially when to this is added the impairment of nutrition necessarily involved by the impoverished condition of the malarial blood. It is interesting to note that, although, as pointed out by Nuttall, the Italian and Tirolese peasantry have long been firmly of the opinion that malaria is transmitted through the mosquito, and although the American, Dr Josiah Nott, in 1848 referred to malaria as if the mosquito theory had already been advanced, little attention was given to this question by most observers. Still earlier, Rasori (in 1846) had stated that " for many years I have held the opinion that intermittent fevers are produced by parasites, which renew the paroxysm by the act of their reproduction, which recurs more or less rapidly according to the variety of the species"; and this appears to be the first well-authenticated reference to this subject. Nuttall, who gives an excellent summary of the literature on the mosquito hypothesis of malaria, assigns to King the honour of again drawing attention to this question. Laveran in 1891, Koch in 1892, Manson in 1894, Bignami and Mendini in 1896, I many facts which, though frequently observed, were very and Grassi in 1898, all turned their attention to this hypothesis. difficult of explanation. Malaria was supposed to be associated Manson, basing his hypothesis upon what he had observed as with watery exhalations and with the fall of dew, but regards the transmission of Filaria by the mosquito, suggested a a wall or a row of trees was seemingly quite sufficient to series of experiments to Major Ronald Ross. These were carried prevent the passage of infection. It was met with on wet out in 1895, when it was found that in mosquitoes that had taken soils, on broken ground, in marshes, swamps and jungles; up blood containing amoeboid parasites, crescents, which were first described as cells, appeared in the stomach-wall after four described as occurring in the red blood corpuscles of the higher animals, increase in size, take up blood pigment, probably from the red corpuscles, and then become developed into sporocytes or gametocytes. The sporocyte is the form which, remaining in the body, ultimately breaks up, as already seen, into a series of minute spores or amoebulae, which in turn go through the same cycle again, increasing in size and forming spores, and so on indefinitely. Gametocytes (the true sexual form) are in certain species, to outward appearance, very similar to the sporocyte, but in others they assume the crescentic shape, and can thus be recognized. The male cell resembles the female-cell very closely, except that the protoplasm is hyaline and homogeneous-looking, whilst that of the female cell is granular. It has already been noted that when the blood is withdrawn from the body certain of the malarial parasites become flagellated. These flagella may be looked upon as sperm elements, which, forming in the male gametocyte, are extruded from that cell, and, once set free, seek out the granular female gametocytes. A single flagellum becomes attached to a small projection that appears on the female cell; it then makes its way into the protoplasm of the female cell, in which rapid streaming movements are then developed. In certain species the female cell is somewhat elongated, and may be peculiarly constricted. It becomes motile, and appears to have the power of piercing the tissues. In this way the first stages of development in the mosquito are passed. The gametocytes, taken along with the blood into the stomach of this insect, pass through the various phases above mentioned, though the zygote form of the human malarial parasite has not yet been traced. In the blood of a patient bitten by an infected mosquito the ordinary malarial parasite may be demonstrated without any difficulty at the end of a week or ten days, and the cycle recommences. This theory, now no longer a hypothesis, in which the mosquito acts as an intermediary host for one stage of the parasite and transmits the parasite to man, affords an ex-planation of many apparently anomalous conditions associated with the transmission of malaria, whilst it harmonizes with on the other hand, it was supposed to be due to the poisonous exhalations from rocks. All this is now explained by the fact or five days; these contained a number of stationary vacuoles that these are the positions in which mosquitoes occur: wherever and pigment granules, ten to twenty in number, bunched to- I there are stagnant pools, even of a temporary nature, mosgether or distributed in lines. Grassi, Bignami and Bastianelli quitoes may breed. It has been observed that although the confirm and supplement Ross's observations; they find that malarial "miasma" never produces any ill effects in patients Anopheles claviger, taking the blood from a patient suffering living at more than a few feet from the surface of the ground, from malaria, soon develops haemosporidia in the intestine. malaria may be found at a height of from 7000 to 9000 ft. above These parasites are then found between the muscular fibres of sea-level; and the fact that a belt of trees or a wall will stop the the stomach; they increase in size, become pigmented, and more passage of the poison is readily explicable on the mosquito and more vacuolated, until they project into the body-cavity. theory. These insects are incapable, owing to their limited power On the sixth day these large spheres contain an enormous of flight, of rising more than a few feet from the ground, and number of minute bodies, refractive droplets like fat, and a cannot make their way through a belt of trees of even moderate diminishing amount of pigment. On the seventh day numerous thickness. Broken ground, such as is found in connexion with filaments, arranged in rows around several foci, are seen. They railway cuttings and canals, may be a focus from which malaria are very delicate, are stained with difficulty, and appear to be may spread. In such broken ground pools are of common perfectly independent of each other, though grouped within a occurrence, and afford the conditions for the development of the capsule. After the capsule has ruptured, these thread-like mosquito, and infected tools used in one area may easily convey " sporozooites," escaping into the body-cavity, gradually make the ova to another. All these facts afford further support of their way to and accumulate in the cells or tubules of the salivary this theory. The conditions of climate under which malaria is glands, whence their passage through the proboscis into the most rife are those which are most suitable for the development human blood is easily understood, of the mosquito. The protection afforded by fires, the recognizes Thus two phases or cycles of existence have been demon- value of mosquito curtains, the simultaneous disappearance strated—one within the human body, the second in the mosquito. of Anopheles and malaria on the complete draining of a neigh-Development That within the human body appears to be capable bourhood, the coincidence of malaria and mosquitoes, and the of the of going on almost indefinitely as long as the patient protection afforded by large expanses of water near walls and Malarial lives, but that in the mosquito appears to be an trees are also important in this connexion. Parasite. offshoot or an intermediate stage. The minute The mosquitoes specially associated with the transmission specks of protoplasm, the amoebulae, which have already been of malaria in the human subject belong apparently to the genu! Anopheles. Anopheles claviger (maculipennis) and Anopheles bifurcatus both are found in Great Britain; Anopheles pictus is another species found in Europe, but so far not in species of Great Britain. A member of the genus Culex, the Mosquito Concerned. grey mosquito or Culex fatigans, is the intermediate host of the proteosoma of birds, on which many of the intermediate phases of the life-history of these parasites have been studied. Ross describes a dappled-wing mosquito as the one with which he performed his experiments on birds in India. Anopheles claviger is interesting in view of the former prevalence of malaria in Great Britain. The remedy for malaria appears to be the removal or spoiling of the breeding grounds of the mosquito, thorough drainage of pools and puddles, or, where this cannot be easily effected, the throwing of a certain amount " of kerosene on the surface of these pools" (Nuttall). Amoebic Dysentery.—In addition to the dysentery set up by bacteria, a form—amoebic dysentery or amoebic enteritis—has been described which is said to be due to an animal parasite, and it has been proposed to separate the various types of dysentery according to their aetiology, in which case the amoebic group is probably more specific than any other. The amoeba (Amoeba dysenteriae, Entamoeba histolytica, of Schaudinn) supposed to give rise to this condition was first described by Losch in 1875. Since then this amoeba has been described either as a harmless parasite or as a cause of dysentery in Europe, Africa, the United States and in Brazil, and more recently in India. This organism, which is usually placed amongst the rhizopods, consists of a small rounded, ovoid or pear-shaped globule of protoplasm, varying in size from 6 to 4oµ, though, as Lafleur points out, these limits are seldom reached, the organism being usually from one and a half to three times the diameter of a leucocyte—from 12 to 26µ (see Plate II., fig. 19). Its margins are well defined, and the body appears to consist of a granular inner portion and a homogeneous outer portion, the latter being somewhat lighter in colour than the inner; in the resting stage this division cannot be made, out. The organism appears to pass through at least two phases, one corresponding to a cystic, the other to an amoeboid, stage. In the latter stage, if the organ-ism be examined on a warm stage, it is seen to send out processes, and, as in other amoebae, vacuoles may be seen as clear spaces lying in the granular and darker-coloured inner protoplasm. In the small vacuoles a deeply stained point may be seen. These vacuoles may be extruded through the ectoplasm. In some cases the vacuoles are so numerous that they occupy the whole of the space usually occupied by the granular protoplasm, and are merely surrounded by a zone of variable thickness, which " has the appearance of finely granular glass of a distinctly pale green tint" (Lafleur). In the cystic stage a nucleus which appears amongst the vacuoles may be made out, usually towards one side of the amoeba. This nucleus is of considerable size, i.e. nearly as large as a red blood corpuscle, and is readily distinguishable from the surrounding protoplasm. When stained by the Benda method(safranin and light green) a more deeply staining nucleolus may be seen in the nucleus. The nucleus is perhaps best seen when stained by this method, but it is always difficult to obtain well-stained specimens of this organism. If these amoebae can be kept under observation for some time evidence of amitotic division may sometimes be seen. Red blood corpuscles are often englobed by this amoeba, as are also micrococci and bacilli. The movements of the amoebae are most active at a temperature of about 90° to 98° F. From the fact that pigment is contained in these organisms, it is supposed that they take in the red blood corpuscles as nutritive material, and that other substances may be taken in to serve a similar purpose. Nothing is known of the method of multiplication of the amoeba, but it is supposed that it may be both by fission and by spore formation. These organ-isms are present in the early stage of the acute disease, and disappear at the later stages. Perhaps of some importance is the fact that the abscesses found in the liver and lung, which occur so frequently in cases of dysentery, usually contain, especially in the portions immediately adjoining the suppurating mass, aconsiderable number of these amoebae. In the very small abscesses the amoebae are numerous and active, and occupy the capillaries in the tissues. It is quite possible that this plugging of the capillaries with amoebae is the cause both of the haemorrhages and of the small areas of necrosed tissue, the supply of nutriment being cut off from the liver cells and from the lung tissues, and that suppuration occurs only as a secondary process, though Councilman and Lafleur maintain that the amoeba itself is the primary cause of suppuration. It is possible, of course, that the suppuration is due to the action of pus-forming organisms conveyed along with, or following, the amoeba, as we know that the growth of suppurating organisms can go on in dead tissues when these organisms have no chance of surviving in the healthy tissues and fluids of the body. Lafleur holds that the amoeba forms a toxic substance which exerts a direct devitalizing effect on the liver cells, and that the amoeba itself causes suppuration. The abscesses in the lung, which invariably extend directly from the liver and occur at the base of the right lung, also contain these amoebae. For these reasons this organism is looked upon as the cause of dysentery and of certain forms of dysenteric abscess. They differ from the Entamoeba coli—often met with in the intestine—which has a more distinct nucleus containing larger chromatin masses and is surrounded by a highly refractile nuclear membrane. Further, in the Entamoeba coll. the cytoplasm is of the same character throughout, there being no differentiation into ectoplasm and endoplasm. The Amoeba histolytica is often met with in a " resting phase," in which the nucleus is less distinctly marked, and may consist of small masses of chromatin distributed throughout the cell or penetrating small buds formed on the surface. Around each of these buds, three, four or more, a highly refractile cyst wall is formed, the cysts becoming separated from the rest of the cell, the remnant of which undergoes disintegration. These cysts are extremely resistant, and probably maintain the continuity of the species outside the body. In the active phase, the amoeboid form appears able by its tough membranous pseudopodia to push its way into the mucous membrane of the large intestine, especially the rectum, the lower part of the ileum and the flexures. Once it is ensconced in these tissues, small soft oedematous looking swellings soon appear on the mucous surface. Marshall points out that the amoebae probably reach the liver by the portal circulation from the dysenteric lesions in which the amoebae are found. Other observers maintain that the amoebae may pass through the walls of the intestine, through the peritoneal cavity, and so on to the liver where they give rise to typical abscesses. Syphilis.—It has long been recognized that syphilis is a specific infective disease, but although characterized by fever, anaemia, and increased growths of tissue followed by rapid degeneration and ulceration of tissue, it is only within quite recent years that a definite parasitic organism, present in all cases of typical syphilis, has been isolated and studied. Schaudinn and Hoffmann, followed by Metchnikoff and others, have described as of constant occurrence a spiral or screw-shaped organism in which are seen from half a dozen to a dozen well-defined, short, regular, almost semicircular curves. This organism, when examined fresh, in normal or physiological salt solution, exhibits active screw-like movements as it rotates along its long axis; from time to time it becomes more or less bow-shaped and then straightens out, the while moving about from point to point in the field of the miscroscope. It is not very strongly refractile, and can only be examined properly with the aid of special central illumination and in the presence of minute particles, by the movements of which the organism is more readily traced. In order to obtain this organism for demonstration it is a good plan to wash the primary or secondary syphilitic sore thoroughly with alcohol; some of the clear fluid is then collected on a cover-glass; or, perhaps better still, the lymphatic gland nearest to one of these sores may be punctured with a hypodermic needle, the fluid being driven out on to a slide on which some normal saline solution has been placed. When the organism has been examined alive the film may be carefully dried and then stained by Giemsa's modification of the Romanowsky stain (see Plate I., fig. I). This stain, which may be obtained ready prepared from Grubler, of Leipzig, under the name of " Giemsa'sche Losung fur die Romanowsky Farbung," is made as follows: Azur II.-eosin compound, 3 grms. and Azur II. 0.8 grm. are mixed and dried thoroughly in the desiccator over sulphuric acid; this mixture is then very finely pulverized, passed through a fine-meshed silk sieve and dissolved at 60° C. in Merck's glycerin, 250 grms., the mixture being well shaken; 25o grms. of methyl-alcohol (Kahlbaum I.), which has been previously heated to 60 C., is then added. The whole, after being well shaken, is allowed to stand for twenty-four hours and filtered. The solution, now ready for use, should be kept in a yellow glass bottle. To i c.c. of ammonia-free distilled water add t drop of this stain. Stain for from a quarter to three-quarters of an hour. Wash in running water, blot, dry, and mount in Canada balsam. Longer exposure to the action of a more dilute Giemsa fluid often gives excellent results. The stained organisms may be seen as delicate, reddish, regular spirals with pointed extremities. They usually measure from 4 to 14µ in length, though they may reach 18 or 22u; the breadth is about 0•25g. In a section of the liver from a case of congenital syphilis an enormous number of these spirochaetes may be found. Stain by Levaditi's method as follows: Fix fragments of tissue not more than i mm. thick in io% formol solution for twenty-four hours. Rinse in distilled water and harden in 96 % alcohol for twenty-four hours. Then wash in distilled water for some minutes, i.e. until the pieces fall to the bottom of the vessel, and transfer to a 1.5-3% solution of nitrate of silver (3% is prefer-able when the tissues have been obtained from the living patient). This impregnation should be carried on at a temperature of 38° C. for from three to five days, according to the nature of the tissue. " Reduce " the silver in the following solution: Pyrogallic acid, 2-4 %, Formol, 5 c.c., Aq. dest., too c.c. Allow this solution to act on the tissues for from twenty-four to forty-eight hours at room temperature. Again wash in distilled water, dehydrate with alcohol, clear with xylol and cedar-oil, and embed in paraffin. The sections should not be more than 5g thick, In a section so stained the spirochaetes are seen as dark spirals standing out against a pale yellow background. On staining with a weak counterstain many of the spirals may be seen actually within the liver cells. This organism may be found in the lung, spleen and other visceral organs, and even in the heart of a patient suffering from syphilis. It has also been found in syphilitic lesions produced experimentally in the higher apes, especially the chimpanzee. As a result of these observations it is now generally accepted as being the primary cause of syphilitic lesions in the human subject. It is certainly present in the lesions usually met with in cases of primary and secondary syphilis of the human subject, and by its action on the blood and tissues of the body produces an antigen, a specific (?) substance, the presence of which has been utilized by Wassermann in the diagnosis of syphilis. He uses the method of deviation of complement by the antigen substances contained in the syphilitic fluid blood or cerebro spinal fluid—by which the lytic action of a haemolysing fluid is prevented. K6la-tzar.—The non-malarial remittent fever, met with in China, known as dum-dum fever in India and as kala-razar in Assam, is associated with peculiar parasitic bodies described by Donovan and Leishman (Herpetomonas Donovani) (? Helcosoma tropicum, Wright). This fever is characterized by its great chronicity, associated with very profound, and ultimately fatal, bloodlessness, in which there is not only a fall in the number of red blood corpuscles, but a marked diminution in the number of white blood corpuscles. Ulceration of the skin and mucous membrane, especially of the lower parts of the small intestine and of the first part of the colon is often present, this being accompanied by dropsy and by distinct enlargement of the liver and spleen. Leonard Rogers, who has given an excellent account of this condition, points out that there is a marked increase in the number of cells in the bone-marrow. The Leishman-Donovan bodies have been found in large numbers, especially in the spleen (see Plate I., fig. 7); they may also be found in the ulcerating surfaces and wherever the cellular proliferation is marked. These organisms may be found in sections, or they may be demonstrated in film preparations made from the material scraped from the freshly-cut surface of the spleen. The films are best stained by Leishman's method: Solution A.—Medicinal methylene-blue (Grubler), 1 part; distilled water, too parts; sodium carbonate, 1.5 parts. This mixture is heated to 65° C. for twelve hours and then allowed to stand at room temperature for ten days. Solution B.—Eosin extra B.A. (Grubler), t part; distilled water, i000 parts. Mix equal parts of solutions A and B in a large open vessel and allow to stand for from six to twelve hours, stirring fr3m time to time with a glass rod. Filter, and washthe precipitate which remains on the paper with a large volume of distilled water until the washings are colourless or only tinged a pale blue. Collect the insoluble residue, dry and pulverize. Make a o.15 % solution of the powder (which may also be obtained from Grubler & Co., Leipzig) in absolute methyl alcohol (Merck's " for analysis "), and transfer to a clean, dry, well stoppered bottle. Pour three or four drops of this stain on to the prepared film (blood, bone, marrow, &c.) and run from side to side. After about half a minute add six or eight drops of distilled water, and mix thoroughly by moving the slide or cover-glass. Allow the stain to act for five minutes longer or, if the film be thick, for ten. Wash with distilled water, leaving a drop or two on the glass for about a minute. Examine at once or after drying without heat and mounting in xylol balsam These peculiar parasitic bodies appear as deeply stained points, rounded, oval or cockle-shaped, lying free or grouped in the large endothelial cells of the spleen. Examined under a magnification of l000 diameters they are found to measure from 3.5 to 2•5µ, or even less, in diameter. Their protoplasm is stained, somewhat unequally, light blue; and from this light blue back-ground two very deeply stained violet corpuscles of unequal size stand out prominently; the smaller of these is more deeply stained than the larger, is thinner, somewhat more elongated or rod-shaped, and parallel or running at right angles to the large corpuscle or obliquely from it. The larger corpuscle is rounded or oval, conical, or sometimes almost dumb-bell shaped. These bodies may appear to touch one another, though usually they are disconnected. Most of these Donovan-Leishman bodies are embedded in the protoplasm of the large endothelial or mono-nuclear splenic cells, of similar cells in the bone marrow, or of certain lymphatic glands. They may also be seen lying in tll protoplasm of the endothelial cells lining the capillary vessels and lymphatics. They are considered by Leishman and Leonard Rogers to be organisms in an intermediate stage of development of either a Trypanosome or some form of Herpetomonas. Rogers, who succeeded in cultivating them outside the body, described changes which he considers are associated with this latter germ. Patton goes further than this, and states that the Leishmania donovani Lay. et Mesn. taken up by the bed bug closely resembles in its life cycle that of the Herpetomonas of the common house-fly. It is thought that the Leishman-Donovan bodies are the tissue parasite stage, and that the herpetomonas stage is probably to be sought for in the blood of the patient. Tsetse-Fly Disease (Trypanosomiasis).—The interesting observations carried out by Sir David Bruce have invested the tsetse-fly with an entirely new significance and importance. In 1895 Bruce first observed that in the tsetse disease—n'gana—there may be found a flagellated haematozoon closely resembling the Trypanosoma Evansii found in Surra. This, like the Surra organism, is very similar in appearance to, but considerably smaller than, the haematozoon often found in the blood of the healthy rat. It has, however, as a rule a single flagellum only. A small quantity of blood, taken from an affected buffalo, wildebeest, koodoo, bushbuck or hyaena—in all of which animals it was found by Bruce—when inoculated into a horse, mule, donkey, cow, dog, cat, rabbit, guinea-pig, rat or mouse, produces a similar disease, the organisms being found sometimes in enormous numbers in the blood of the inoculated animal, especially in the dog and in the rat. He then found that the tsetse-fly can produce the disease in a healthy animal only when it has first charged itself with blood from a diseased animal, and he produced evidence that Glossina morsitans is not capable of producing the disease except by carrying the parasites from one animal to another in the blood that it takes through its proboscis into its stomach. The parasites taken in along with such blood may remain in the stomach and alive for a period of 118 hours, but shortly after that the stomach is found to be empty, and the parasites contained in the excrement no longer retain their vitality. The mode of multiplication of these organisms has been studied by Rose-Bradford and Plimmer, who maintain that the multiplication takes place principally in the spleen and lymphatic glands. The tsetse-fly parasite, however, is still imperfectly understood, though much attention is now being paid to its life-history and development. Sleeping Sickness (Try panosorniasis) .—To the group of diseases caused by Trypanosomes must now be added sleeping sickness. This disease is due to the presence and action in the human body of a form known as T. gambiense (Dutton). In order to demonstrate the parasite in the blood of a case of sleeping sickness, where they are very scanty and difficult to find, the best method is repeated centrifugalization of the blood (Bruce), ro c.c. being treated at a time; then the sediment in a number of these tubes is collected and again centrifugalized. The living trypanosome may, as a rule, be distinguished in this final sediment, even under a low power of the microscope. The organism may be found in greater numbers in the cerebro-spinal fluid of a case in which the symptoms of sleeping sickness have been developed, though centrifugalization of from ro• to 15 c.c. of the cerebro-spinal fluid for half an hour may be necessary before they can be demonstrated. Greig and Gray, at Mott's suggestion, were able to find the organism in the fluid removed by means of a hypodermic syringe from the swollen lymph glands that appear as one of the earliest signs of infection. Examined fresh and in its native fluid or in normal saline solution it is seen as an actively motile, highly'refractile, somewhat spindle-shaped organism (see Plate I., fig. g). The anterior end is prolonged into a pointed flagellum, the posterior end being slightly blunted or rounded. This organism darts about rapidly between the red blood corpuscles or other corpuscles or particles, and shows rapid undulations, the flagellum beating quickly and the body following the flagellum. In this body a couple of very bright points may be seen. On staining by Leishman's stain (see under Kola-dear) the general protoplasm of the body is stained blue and is somewhat granular. This trypanosome is from 15 to 2511 in length (without the flagellum, which is from 5 to 6µ) and from 1.5 to 2' sµ broad. In the centre of the spindle-shaped mass is a very distinct reddish purple oval corpuscle corresponding to the larger of the two bright points seen in the unstained specimen; this, the nucleus or macronucleus, is slightly granular. Near the posterior or blunt end of the organism is a second, but much smaller, deeply stained reddish purple point, the second of the bright spots seen in the unstained specimen; this is known as the micro-nucleus or centrosome. Around the micro-nucleus is a kind of court or area of less deeply stained protoplasm, arising from or near which and running along the margin of the body is a narrow band with a very sharply defined wavy free margin. This thin band of protoplasm seems to be continuous with the large spindle-shaped body of the trypanosome, but at the free margin it takes on the red tint of the micro-nucleus instead of the blue tint of the protoplasm. The undulatory membrane, as this band is called, is narrowest at the posterior end, getting broader and broader until the micro-nucleus is reached, beyond which it tapers off irregularly until finally it merges in the flagellum. In sleeping sickness the presence of this organism is usually associated with distinct anaemia, the red cells being diminished in number and the haemoglobin in quantity. Along with this there is an increase in the number of mononuclear leucocytes. The trypanosome is carried to the human patient by the Glossina pal palls, in the proboscis of which the organ-isms may be seen for some short time after the insect has sucked blood from an infected patient. These trypanosomes have been found living and active in the stomach of this insect up to 118 hours, but after 140 hours no living parasites can be demonstrated. They undergo no metamorphoses in this intermediate host and are simply discharged in the intestinal excreta. It may be readily understood that the trypanosome under these conditions soon loses its virulence, and an animal cannot be infected through the bite of the Glossina for more than 48 hours after the infected blood has been ingested by the fly. The organism may remain latent in the human body for a considerable period. It certainly sets up very tardily any changes by which its presence can be detected. The first symptoms of its presence and activity are enlargement of the lymphatic glands, especially those behind the neck, a condition often accompanied by irregular and intermittent fever. After a time, in from three months to three years, according to Bruce, the organism gains access to the fluid in the cerebrospinal canal. Accompanying this latter migration are languor, lassitude, a gradually increasing apathy, and finally profound somnolence. The incubation period, or that between the time of infection and the appearance of the symptoms associated with trypanosomiasis may be as short as four weeks, or it may extend over several years. The inhabitants of the island of Senegal who have lived in Casamance do not consider themselves safe from the disease until at least seven years after they have left an infected area. At first, amongst negroes, according to Dutton and Todd, there is no external clinical sign of disease except glandular enlargement; in mulattoes and whites an irregular and intermittent fever may be the chief sign of infection, " the temperature being raised for two to four days, then falling to normal or below normal for four or five days." In other cases the fever is of the septic type, the temperature being normal in the morning but rising in the evening to 101.3° or 102.20 F., rarely to 1040 F., the curve differing from that characteristic of malaria in which the rise usually takes place in the morning. Moreover, in sleeping sickness there are no rigors before the rise of temperature and but slight sweating, such as there is usually occurring at the end of the rise. Here again we have a distinction between the malarial condition and that of sleeping sickness. The respiration and the pulse rate are increased both during the febrile and the non-febrile attacks; the respiration is from 29 to 30 a minute, and the pulse rises to go, and even up to 140, a minute, according to the degree of cardiac excitability which appears to be constantly present. The localized swelling and redness are seen as puffiness of the face, oedema of the eyelids and ankles and feet, congested erythematous patches on the face, trunk or limbs. Anaemia, general weakness and wasting, at first very slightly marked, gradually become prominent features, and headache is often present. The enlargement of the spleen appears to go on con-currently with enlargement of the lymphatic glands. Manson points out that trypanosomiasis may terminate fatally without the appearance of any characteristic symptoms of sleeping sickness, but as a rule the " sleeping " or second stage supervenes. The temperature now becomes of the hectic type, rising to 102.2° F. in the evening and falling to 98.6° F. in the morning. Here again there are no rigors or sweating. During the last stages of the disease the rectal temperature may fall as low as 95° and for the last day or two to 92° F., the pulse and respiration falling with the temperature. The irritability of the heart is still marked. Headache in the supraorbital region, and pain in the back, and even in the feet, have been described. Activity and intelligence give place to laziness, apathy and dullness; the face loses its brightness, the eyelids approximate, and the muscles around the mouth and nose become flabby and flaccid, the patient becomes drowsy, and when questioned replies only after a marked interval. Fibrillary tremors of the tongue and shaking of the hands and arms, distinct even during rest, become increased when any voluntary movement is attempted. These tremors may extend to the lower limbs and trunk. Epileptiform convulsions, general weakness and progressive emaciation come on, and shortly before death there is incontinence of urine and faeces. "The intellectual faculties gradually become impaired, the patient has a certain amount of difficulty in understanding what is said to him, and becomes emotional, often crying for no reason whatever; delirium is usually absent, the drowsiness increases and the patient's attitude becomes characteristic, the head falls forward on the chest and the eyelids are closed. At first the patient is easily aroused from this drowsy condition, but soon he reaches a stage in which he falls sound asleep almost in any attitude and under any conditions, especially after meals. These periods of sleep, which become gradually longer and more profound, lead eventually to a comatose condition from which the patient can be aroused only with the greatest difficulty. It is at this stage that the temperature becomes normal and death occurs." Nabarro points out, however, that this condition of drowsiness and sleep, leading eventually to coma, is by no means invariably present. In the early part of the sleeping-sickness stage patients often sleep more than usual, but later do not sleep excessively. They become lethargic and indifferent to their surroundings, however, and often lie with their eyes closed. When spoken to they hear and understand what is said to them and after a longer or shorter interval give a very brief reply. The leucocytosis that occurs during the course of this form of trypanosomiasis is due, apparently, to secondary or terminal bacterial infections so frequently associated with the disease in its later stages. The first stage of the disease, that of fever, may last for several years; the second or nervous stage with tremors, &c., for from four to eight months. It is quite exceptional for the disease to be prolonged for more than a year from the time that the nervous symptoms become manifest, though a European who contracted trypanosomiasis in Uganda, having delusions and becoming drowsy within the year, did not die of sleeping sickness until more than eighteen months from the onset of the nervous symptoms. The Glossina palpalis is not found in swamps. It affects a belt of from ten to thirty yards broad along banks bounding water shaded by scrub and underwood. It may, however, follow or be carried by the animal or human subject it is attacking for a distance of, say, three hundred yards, but unless carried it will not cross an artificial clearing of more than thirty yards made in the natural fly belt. The authorities in the plague-stricken areas recommend, therefore, the clearance of belts thirty yards in width along portions of the lake side, at fords and in such other places as are frequented by natives. No infected person should be allowed to enter a " fly area," so that they may not act as centres from which the flies, acting as carriers, may convey infection. The provision of clothing for natives who are compelled to work in fly areas is an important precautionary measure. There seems to be some doubt as to whether Trypanosoma gambiense of Dutton is the same organism and produces the same conditions as the Trypanosoma of Bruce and Nabarro from Uganda, but most observers seem to think that the two species are the same and yield the same results when inoculated into animals. It is supposed that this trypanosome may pass through certain stages of metamorphosis in the human or animal body, and different drugs have been recommended as trypanocides during these various stages, an arsenic preparation (atoxyl) first being given, and then, when the organisms have disappeared, injections of bichloride of mercury, this salt appearing to prevent the relapses which occur when atoxyl only is given over a prolonged period. Ehrlich, treating animals suffering from trypanosomiasis with parafuchsin, found that although the parasites disappeared from the blood they soon recurred. On the exhibition of another dose of parafuchsin they again disappeared. This was repeated for a considerable number of times, but after a time the parafuchsin lost its effect, the trypanosome having acquired an immunity against this substance; they had in fact become " fuchsin-fast." Such fuchsin-fast organisms injected into animals still retain their immunity against parafuchsin and may transmit it through more than Too generations. Nevertheless, they cannot withstand the action of other trypanocidal drugs. The outcome of all this is that large doses of the trypanocidal drug should be given at once, and that the same drug should never be given over too long a period, a fresh drug often being effective even when the first drug has lost action. II.—To OTHER ANIMAL PARASITES Filariasis.—Since Bancroft and Manson first described Filaria nocturna and its relation to the common form of filariasis, the most important contribution to our knowledge has been made, at the suggestion of the younger Bancroft, by Dr G. C. Low, who has demonstrated that the embryos of the filaria may be found in the proboscis of the mosquito (Culex ciliaris), whence they probably find their way into the circulating blood of the human subject. Lt appears that the filaria embryo after being taken, with the blood of the patient, into the stomach of the mosquito, loses its sheath; after which, leaving the stomach, it passes into the thoracic muscles of its intermediate host, and becomes more fully developed, increasing considerably in size and attaining a mouth, an alimentary canal, and the characteristic trilobed caudal appendage. It now leaves the thoracic muscles, and, passing towards the head, makes its way " into the loose cellular tissue which abounds in the prothorax in the neighbourhood ofthe salivary glands." Most of them then " pass along the neck, enter the lower part of the head," whence they may pass into the proboscis. Although it has never been demonstrated that the filaria is directly inoculated into the human subject from the proboscis of the mosquito, it seems impossible to doubt that when the mosquito " strikes," the filaria makes its way into the circulation directly from the proboscis. It is important to note that the mosquito, when fed on banana pulp, does not eject the filaria from its proboscis. This, however, is not to be wondered at, as the filaria is apparently unable to live on the juices of the banana; moreover, the consistence of the banana is very different from that of the human skin. The importance of this observation, as affording an additional reason for taking measures to get rid•of the mosquito in districts in which filariasis is rife, can scarcely be over-estimated. C .—Infective Diseases in which an Organism has been found, but has not finally been connected with the Disease. Hydrophobia is usually contracted by man through inoculation of an abraded surface with the saliva of an animal affected with rabies—through the bite of a dog, the animal in which the so-called rabies of the streets occurs. The puppy is specially dangerous, as, although it may be suffering from rabies when the saliva contains an extremely exalted virus, the animal may exhibit no signs of the disease almost up to the time of its death. The other animals that may be affected " naturally " are wolves, cats, foxes, horses, cows and deer; but all warm-blooded animals may be successfully inoculated with the disease. The principal changes met with are found in the nervous system, and include distension of the perivascular lymphatic sheaths, congestion and oedema of the brain and spinal cord and of the meninges. Haemorrhages occur into the cerebral ventricles of the brain, especially in the floor of the fourth, and on the surface and in the substance of the medulla oblongata, and the spinal cord. In addition to these small haemorrhages, collections of leucocytes are met with in hyperaemic areas in the medulla oblongata and pons, sometimes in the cortical cerebral tissue and in the spinal cord, in the perivascular lymphatics of the grey matter of the anterior horns and in the white matter of the postero-internal and postero-external columns. Here also the nerve cells are seen to be vacuolated, hyaline and granular, and often pigmented; thrombi may be present in some of the smaller vessels, and the collections of leucocytes may be so prominent, especially in the medulla, that they have been described as miliary abscesses. Haemorrhages are also common in the various mucous and serous membranes; hyaline changes in and around the walls of blood-vessels; proliferation of the endothelium; swelling and vacuolation of nerve cells; pericellular infiltration with leucocytes, and infiltration of the salivary glands with leucocytes (Coats). An increased number of leucocytes and microcytes in the blood has also been made out. The virus, whatever it may be, has a power of multiplying in the tissues, and of producing a toxic substance which, as in the case of tetanus toxin, appears to act specially on the central nervous system. In recent years fresh interest has been aroused in the morbid histology of the brain and cord in hydrophobia by the appearance of Negri's description of " bodies " which he claims are found in the central nervous system only in hydrophobia or rabies (see Plate I., fig. 3). These bodies, which are rounded, oval, triangular, or slightly spindle- or sausage-shaped, when specially stained consist of a red (acidophile) basis in which stand out small blue (basophile) granules, rods and circles, often situated within vacuoles. A small central point which is surrounded by no clear space is supposed to correspond to the nucleus of a protozoan. But this can be little more than a suggestion. The Negri bodies are certainly present in the central nervous system in cases of hydrophobia, and have not been found in similar positions in any other disease. They are present in large numbers, even at an early stage of the disease, although they are then so small that they may easily escape detection, so small indeed that they may pass through the pores of a Berkefeld filter, the filtrate in such cases being capable of acting as a rabic virus. In the more chronic cases and in the later stages of the disease the Negri bodies may attain a considerable size and may be easily seen under the microscope. They are from o•5µ to 20µ in diameter—the longer the course of the disease the larger the bodies, these larger forms seldom if ever being met with in specially susceptible animals, which soon succumb to the disease. The Negri bodies may be constricted in the middle, or; if some-what elongated, there may be two or three constrictions which give it the appearance of a string of sausages. They may be met with in almost all the nerve cells of the central nervous system in well-developed cases of hydrophobia, but they are most numerous and are found most readily in the cells of the cornu ammonis, and then in the Purkinje cells of the cerebellum. Although there are several methods of preparing these organisms for microscopical examination, the following is perhaps the simplest. A fragment of the grey substance, say from the cornu ammonis, is taken from a section made at right angles to the surface and placed on a slide about one inch from the end. A coverslip is now " pressed upon it until it is spread out in a moderately thin layer; then the coverslip is moved slowly and evenly over the slide," leaving the first three-quarters of an inch of the slide clear. In making the smear only slight pressure is used, the pressure beginning on the edge of the coverslip away from the end of the slide towards which the coverslip is travelling, thus driving more of the nerve tissues along the smear " and producing more well-spread nerve cells." The smears are then air-dried, placed in methyl-alcohol for one minute, and then in a freshly-prepared mixture of io c.c. of distilled water, three drops of a saturated alcoholic solution of rose anilin violet, and six drops of Loeffler's alkaline methylene blue, which is warmed until steam rises; the stain is then poured from the specimen, which after being rinsed in water is allowed to dry and is then mounted in Canada balsam. The nature of the disease produced by the inoculation of saliva from a rabid animal appears to depend upon (r) the quantity of the rabic virus introduced; (2) the point of its introduction; (3) the activity of the virus. Thus by diluting the poison with distilled water or saline solution and injecting small quantities, the period of incubation may be prolonged. Slight wounds of the skin, of the limbs and of the back are followed by a long incubation period; but when the inoculation takes place in the tips of the fingers or in the skin of the face, where nerves are numerous, and especially where the wound is lacerated or deep, the incubation period is much shorter and the attack usually more severe. This, as in tetanus, is accounted for by the fact that the lymphatics of the nerves are much more directly continuous with the central nervous system than are any other set. of lymphatics. The poison appears to act directly upon the cells of the central nervous system. Arising out of recent researches on hydrophobia, two methods of treatment—one of which, at any rate, has been attended by conspicuous success—have been put into practice. The first of these, Pasteur's, is based upon the fact that rabic virus may be intensified or attenuated at will. Pasteur found that although the virus taken from the cerebrospinal fluid of the dog always produces death in the same period when inoculated into the same animal, virus taken from other animals has not the same activity. If passed through a succession of monkeys it may become so attenuated that it is no longer lethal. If either the " monkey virus," which is not fatal to the rabbit, or the " dog virus," which kills in twelve to fourteen days, be passed through a series of rabbits, the virulence may be so exalted that it may kill in about six days: its activity cannot be increased beyond this point by any means at present at our disposal. This intensified virus was therefore named virus fixe by Pasteur, and it forms a standard from which to work. He found, too, that under certain conditions of temperature the virus may be readily attenuated, one hour at 500 or half an hour at 6o° C. completely destroying it. A 5% solution of carbolic acid acting for half an hour, or a r per moo solution of bichloride of mercury or acetic acid or permanganate of potash, brings about the same result, as do also exposure to air and sunlight. The poison contained in the spinal cord of the rabbit exposed to dry air and not allowed to undergo putrefactive changes gradually loses its activity, and at the end of fourteen to fifteen days is, incapable of setting up rabic .symp-toms. A series of cords from rabbits inoculated with the virus fixe are cut into short segments, which, held in series by the dura mater, are suspended in sterile glass flasks plugged with cotton-wool and containing a quantity of potassium hydrate—a powerful absorbent of water. At the end of twenty-four hours the activity of the virus is found to have fallen but slightly; at the end of forty-eight hours there is a still further falling off, until on the fourteenth or fifteenth day the virus is no longer lethal. With material so prepared Pasteur treated patients who had been bitten by mad dogs. On the first day of treatment small quantities of an emulsion of the cord exposed for thirteen or fourteen days in saline solution are injected subcutaneously, and the treatment is continued for from fifteen to twenty-one days, according to the severity of the bite, a stronger emulsion—i.e. an emulsion made of a cord that has been desiccated for a shorter period—being used for each succeeding injection, until at last the patient is injected with an emulsion which has been exposed to the air for only three days. In the human subject the period of incubation of the disease is comparatively prolonged, owing to the insusceptibility of the tissues to the action of this poison; there is therefore some chance of obtaining a complete protection or acclimatization of the tissues before the incubation period is completed. The virus introduced at the bite has then no more chance of affecting the nerve centres than has the strong virus injected in the late stages of the protective inoculation: the nerve centres, having become gradually acclimatized to the poisons of the rabic virus, are able to carry on their proper functions in its presence, until in time, as in the case of microbial poisons, the virus is gradually neutralized and eliminated from the body. Various modifications and improvements of this method have from time to time been devised, but all are based on, and are merely extensions of, Pasteur's original work and method. As soon as it was found that antitoxins were formed in the tissues in the case of an attack of tetanus, attention was drawn to the necessity of determining whether something similar might not be done in the production of an antirabic serum for the treatment of rabies. Babes and Lepp, and then Tizzoni and his colleagues Schwarz and Centanni, starting from virus fixe, obtained a series of weaker inoculating materials by submitting it for different periods to the action of gastric juice. Beginning with a weak virus so prepared, and from time to time injecting successively stronger emulsions (seventeen injections in twenty days) into a sheep, they succeeded in obtaining a serum of such antirabic power that if injected in the proportion of r to 25,000 of body-weight, an animal is protected against a lethal dose of virus fixe. The activity of this serum is still further reinforced if a fresh series of injections is made at intervals varying from two to five months, according to the condition of the animal, each series occupying twelve days. This antirabic substance stored in the blood has not only the power of anticipating (neutralizing?) the action of the poison, but also of acting as a direct curative agent; as a prophylactic agent, readily kept in stock and easily and rapidly exhibited, it possesses very great advantages over the inoculation method. It must be borne in mind that the longer the period after the infection the greater must be the amount of serum used to obtain a successful result. As regards the necessity for any treatment it may be pointed out that although the saliva of a rabid dog may be infective three days before the manifestation of any symptoms of the disease death takes place almost invariably within six days of the first symptom. If therefore the animal remains alive for ten days after the patient is bitten, there is no necessity for the antirabic treatment to be applied and the patient need fear no evil results from the bite. There can be little doubt that hydrophobia is a specific disease due to a multiplication of some virus in the nervous system, in the elements of which it is ultimately fixed; that it passes from the wound to the central nervous system by the lymphatics; and that, as in tetanus, the muscular spasms are the result of the action of some special poison on the central nervous system. Scarlet Fever.—In scarlet fever recent observations have been comparatively few and unimportant. creoke, and later Klein, and others have, however, shown that in the glands and throats of scarlet fever patients a streptococcus, to which is assigned the chief aetiological role in connexion with this disease, is present. On the other hand, it is maintained by many observers that these streptococci are nothing more than the streptococci found in puerperal fever, erysipelas, and similar infective conditions, and certainly the organisms described closely resemble Streptococcus pyogenes. In 1904 Mallory described certain " bodies " which he considers may be associated with scarlet fever, and which were sufficiently distinctive to justify him in suggesting that he was dealing with the " various stages in the developmental cycle of a protozoan." These bodies, which were demonstrated in four cases of scarlet fever, " occur in and between the epithelial cells of the epidermis and free in the superficial lymph vessels and spaces of the corium." They are small, varying from the size of a blood platelet to that of a. red blood corpuscle, and " stained delicately but sharply with methylene blue." Well formed rosettes with numerous segments may be seen, forms which Mallory thinks may correspond to the phase of asexual development of the malarial parasite. He also describes " coarsely reticulated forms which may represent stages in sporogony or be due to degeneration of the other forms." He gives beautiful illustrations, both drawings and photographs, of these organisms, and without claiming that he has proved any aetiological relation between these bodies and scarlet fever, states that his personal opinion is that such relation exists. D.—Infective Diseases not yet proved to be due to Micro-organisms. Small-pox.—There have been few recent additions to our knowledge of the aetiology of small-pox, though Dr Monckton Copeman now holds that the small-pox organism, like that of vaccine, is probably a very minute bacillus, which, from its behaviour in the presence of glycerin, is possessed of the power of forming spores. If vaccine lymph, taken from the calf, be protected from all extraneous sporebearing organisms and treated with 50 % solution of glycerin, it, in time, becomes absolutely sterile as regards ordinary non-sporebearing organisms. Even the staphylococci and streptococci, usually found in calf lymph, cannot withstand the prolonged action of this substance, but spore-bearing organisms still remain alive and active. Moreover, the lymph still retains its power of producing vaccine vesicles, so that the vaccine organism, in its powers of resistance, resembles the spore-bearing, and not the non-sporebearing, organisms with which we are acquainted. This vaccine organism must be very minute; it is stated that it can be cultivated only on special media, though it multiplies freely in the superficial cutaneous tissues of the calf, the monkey and the human subject. Perhaps the most important outcome of Dr Monckton Copeman's work on this subject is that he has obtained a vaccine lymph from which are eliminated all streptococci and staphylococci, and, if the lymph be taken with reasonable care, any other organisms which could possibly give rise to untoward results. Typhus Fever.—Although it is fully recognized that typhus must be one of the specific infective fevers brought about by the action of a special micro-organism, no definite information as to the bacterial aetiology of this condition has been obtained. It is always looked upon as a " filth " disease; and from the frequency of minute haemorrhages, and from the resemblance to the haemorrhagic septicaemias in other respects, it appears probable that the bacillus of typhus is the organism described by Mott in 1883 as an actively motile dumb-bell coccus, and ten years later by Dubieff and Bruhl as the Diplococcus typhosus exanthematicus; the polar staining and general resemblance to the diplococcus of fowl cholera, the plague bacillus, the diplococcus of " Wildseuche," certain forms of swine fever and hog cholera, and others of the haemorrhagic septicaemias, are sufficient to suggest the generic affinity of this organism to this septicaemic group. We have as yet, however (1910), no absolute proof of the aetiological relation of the bacillus to this disease. Measles.—In measles, as in scarlet fever, micrococci have had ascribed to them the power of setting up the specific disease. Canon and Pielicke have, however, described minute bacilli somewhat resembling those described as occurring in vaccine lymph. These are found in the blood in the early stages of the disease, and also in the profuse catarrhal secretions so characteristic of this condition. There are no records of the successful inoculation of this minute bacillus, and until such evidence is forthcoming this organism must be looked upon as being an accessory, possibly, but not the prime cause, of measles. Mumps.—It is generally accepted that mumps is probably caused by a specific micro-organism, the infective material making its way in the first instance through the ducts to the parotid and other salivary glands. It appears to bring about a peculiar oedematous inflammation of the interstitial tissue of the glands, but slight parenchymatous changes may also be observed. The virus is present in the tissues for some days before there is any manifestation of parotid swelling, but during this period it is extremely active, and the disease may be readily transmitted from patient to patient. The infectivity continues for some time, probably for nearly a week after naked-eye manifestations of the diseased condition have disappeared. Whooping-Cough.—A diplococcus, a streptococcus, and various higher fungi have in turn been put down as the cause of this disease. It must, from its resemblance to the other specific infective fevers, be considered as an infective disease of microbic origin, which goes through a regular period of incubation and invasion, and in which true nervous lesions, especially of the pneumogastric and superior laryngeal nerves, are somewhat common. Affanassieff, and later Koplick, have described a minute bacillus, with rounded ends and bi-polar staining, which occurs in the mucus discharged at the end of a paroxysm of whooping-cough. Koplick examined sixteen cases, and found this organism in thirteen of them. There can be little doubt that the infective material is contained in the expectoration. It may remain active for a considerable period, but is then usually attached to solid particles. It is not readily carried by the breath, and multiplies specially in the mucous membranes, setting up inflammation, probably through its toxic products, which appear to be absorbed, and, as in the case of the tetanus poison, to travel specially along the lymphatics of the local nerves. Affections of the lung—bronchitis and broncho-pneumonia—may be directly associated with the disease, but it is much more likely that these affections are the result of secondary infection of tissues already in a weakened condition. Au-mom-rms.—General: Allbutt and Rolleston, System of Medicine (2nd ed., London, 1905 et seq.) ; Castellani and Chalmers,Manual of Tropical Medicine (London, 191o) ; Fischer, The Structure and Functions of Bacteria, trans. by K. Coppen Jones (Oxford, 1900); Manson, Sir P., Tropical Diseases (3rd ed., London, 1903) ; Nuttall, " On the Role of Insects, &c., as carriers in the spread of bacterial and parasitic diseases of man and animals " (Johns Hopkins Hospital Reports, viii., 1899) ; Schneidemuhl, Lehrb. d. vergleich. Path. u. Therapie d. Menschen u. d. Hausthiere (Leipzig, 1898) ; Woodhead, Bacteria and their Products (London, 1891). Actinomycosis: Bostrom, Ziegler's Beitr. z. pathol. Anatomie, Bd. ix. (1891); Illich, Beitrag z. Klinik d. Actinomykose (Vienna, 1892); M'Fadyean, Journ. Compar. Path. and Therap., vol. ii. (1899). Cerebro-Spinal Meningitis: Councilman, Mallory and Wright, Rep. Bd. Health, Mass. (Boston, 1898) ; Davis, Journ. Infect. Diseases, iv. 558 (19o7); Mackenzie and Martin, Journ. Path. and Bacteriol. xii. 539 (1908) ; Ruppel, Deutsche med. Wochenschr., S. 1366 (1906); Shennan and Ritchie, Journ. Path. and Bacterial. xii. 456 (1908); Symmers and others, Brit. Med. Journ. ii. 1334 (1908). Cholera: Dunbar, in Lubarsch u. Ostertag's Ergebn. d. allg. Pathologie, vol. i. (1896). Diphtheria: Behring, " Die Geschichte d. Diphtherie " (Leipzig, 1893), and various other papers, principally in Zeits. f. Hygiene, Bd. xii. (1892) onwards; Ehrlich, " Die Werthbemessung d. Diphtherieheilserums u. d. theoret. Grundlagen," Klinisches Jahrb., Bd. vi. (1897); Klebs, " Ueber Diphtherie," Verh. d. II. Congr. f. inn. Med. in Wiesbaden (1883); Loeffler, " Unters. u. d. Bedeut. d. Mikro-org. f. d. Entst. d. Diphtheritis b. Menschen, &c.," Mitth. a. d. k. Gesundheitsamcte, Bd. ii. (1884); Martin, Sidney, Goulstonian Lectures, Brit. Med. Journ. vol. i. (1892) ; Nuttall and Graham Smith, The Bacteriology of Diphtheria (Cambridge, 1908); Roux and Yersin, " Contrib. a 1'6tude d. 1. Dipht6rie," Annales de l'inst. Pasteur, t. ii.–iv. (1888-189o). Dysentery: Kartulis, " Die Amoebendysenterie," in Kolle and Wassermann's Handb. d. path. Mikro-org. Erga,nz. Bd. p. 347 (1906) ; Osler, " On the Amoeba coli in Dysentery and in Dysenteric Liver Abscess," Johns Hopkins Hosp. Bull. vol. i. (189o). Erysipelas: Coley, Proc. Roy. Soc.Med. (London, 1909), vol. iii. (Surg. Sect.), p. 1; Fehleisen, Aetiologie der Erysipels (Berlin, 1883). Filariasis: Low, " On Filaria Nocturna in ` Culex,' " Brit. Med. Journ. vol. i. (1900) ; Manson, Tropical Diseases (3rd ed., London, 1903). Gonorrhoea: Bumm, Der Mikro-organismus d. gonorrh. Schleimhaut-Erkrankungen (Wiesbaden, 1885); See, Le Gonocoque (Paris, 1896). Glanders: Koranyi, in Nothnagel's Specielle Pathologie, Bd. v. (1897); Loeffler and Schutz, Deutsche med. Wochenschr. (1882, Eng. trans., 1886); M'Fadyean, " Pulmonary Lesions of Glanders," Journ. Comp. Path. and Therap, vol. (18e)5); Journ. State Medicine, pp. 1, 65, 72, 125 (1905). Hydrophobia: Babes and Lepp, " Rech. s. 1. vaccination antirabique," Ann. de l'inst. Pasteur,, t. iii. (1889) ; Hogyes, in Nothnagel's Specielle Pathologie, Bd. v. (1897); Negri, Boll. soc. med. chic. di Pavia, Nos. 2, 4 (1903); Ztschr. f. Hyg., Bd. xliii. S. 507, Bd. xliv. S. 519 (1903); Pasteur, Traitement de la rage (Paris, 1886), and numerous papers in the Compt. rend. acad. d. sc. (Paris, from 1881 onwards), and in Ann. de l'inst. Pasteur, t. i. (1887) and t. ii. (1888) ; Tizzoni and Centanni, Lancet, vol. ii. (1895). Influenza: Canon, " Ueber einen Mikro-org. i., Blute v. Influenzakranken," Deutsche med. Wochenschr. (1892); Pfeiffer, " Vorl. Mitth. u. d. Erreger d. Influenza," Deutsche razed. Wochenschr. (1892). RA1a-Azar: Laveran et Mesnil, Corn pt. rend. acad. d. sc. cxxxvn. p. 957 (Paris, 1903) ; Leishman, in Allbutt and Rolleston's Syst. Med. vol. ii., pt. ii. p. 226 (2nd ed., London, 1909); Patton, Scientific Memoirs Gov. India, No. 27 (1907), No. 31 (1907) ; Rogers, Brit. Med. Journ. i. 427, 490, 557 (1907). Leprosy: Hansen and Looft, Leprosy in its Clin. and Path. Aspects, trans. by N. Walker (Bristol, 1895) ; Mitth. u. Verhandl. d. internat. wissensch. Lepra-Conferenz z. Berlin (1897); Rake, Reports of the Trinidad Asylum. (1886—1893); Report of the Leprosy Commission to India (1893). Mycetoma or Madura Foot: Bocarro, " Analysis of too Cases of Mycetoma," Lancet, vol. ii. (1893); Boyce and Surveyor, Proc. Roy. Soc. Lond. vol. liii. (1893); Vandyke Carter, Trans. Path. Soc. Lond. vol. xxiv. (1873), and " On Mycetoma or the Fungus Disease of India " (London, 1874) ; Kanthack, Journ. Path, and Bact. vol. i. (1892) ; Lewis and Cunningham, Physiol. and Pathol. Researches (1875) ; " Fungus Disease of India," Quain's Dict. of Medicine, vol. i. (1894); Unna and Delbanco, Monats. f. prakt. Derm. Bd. xxx., S. 545 (1900) ; Vincent, " Et. s. 1. parasite d. pied Madure," Ann. de l'inst. Pasteur, t. viii. (1894). Malaria: Celli, Malaria, trans. by Eyre (London, 1900) ; Nuttall, " Neuere Forsch. ii. d. Rolle d. Mosquitos, &e.," Centralbl. f. Bact. u. Parasitenk. Abt. I. (1900), and in .Tourn. Trop. Med. vols. ii., iii. (1900), and Journ. Hyg. vols. i., ii. (19oi) ; Nuttall and Shipley, Journ. Hyg. i. 4, 45, 269, 451 (1901), ii. 58 (1902); Ruge in Kolle and Wassermann's Handb. d. path. Mikro-org. Erganz. Bd. (Jena, 1907). Malta Fever: Bruce, Note on the Discovery of a Micro-organism in Malta Fever," Practitioner (1887) ; " Obs. on Malta Fever," Brit. Med. Journ. vol. i. (1889) ; " Malta Fever," in Davidson's Hygiene of Warm Climates (Edinburgh, 1893) ; Eyre, Quart. Journ. 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Xi., and (1898) t. xii.; Durham and Myeers, " Interim Report on Yellow Fever," Brit. Med. Journ. (1901), i. 450. (G. S. W.)
PARASITE (From Gr. irapa, beside, Tiros food)

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