NUTRITION  . The See also:

• PHYSIOLOGY (from Gr. 4 i s, nature, and koyos, discourse)

physiology of nutrition involves the study of the way in which the tissues of the See also:

• BODY

body, and more especially the See also:

• GREAT

great See also:

• MASTER (Lat. magister, related to tnagis, more, as the corresponding minister is to minus, less; the English form is due partly to the O. Eng. maegister, and partly to O. Fr. maistre, mod. maitre; cf. Du. meester, Ger. Meister, Ital. maestro)

master tissues, muscle and See also:

• NERVE (Lat. nervus, Gr. vevpov, a bowstring)

nerve, obtain the material for growth and repair and the See also:

• ENERGY (from the Gr. ivipyela; iv, in, ipyov, work)

energy for See also:

• MECHANICAL

mechanical See also:

• WORK

work and See also:

• HEAT (0. E. haktu, which like " hot," Old Eng. hat, is from the Teutonic type haita, hit, to be hot; cf. Ger. hitze, heiss; Dutch, hitte, heet, &c.)

heat See also:

• PRODUCTION (Lat. productionem, from producere, to pro-duce)

production, and of the mode in which they get rid of the See also:

• WASTE (O. Fr. wast, guast, gast, gaste; Lat. vastus, vast, desolate)

waste products.of their activity . The study is therefore very largely a study of the See also:

• HISTORY

history of the See also:

• FOOD
• FOOD (like the verb " to feed," from a Teutonic root, whence O. Eng. foda; cf. " fodder "; connected with Gr. lrareicOae, to feed)

food of the body, since it is in the food that the necessary See also:

• MATTER

matter and energy are supplied . Under See also:

• DIETETICS

DIETETICS the See also:

• COMPOSITION
• COMPOSITION (Lat. compositio, from componere, to put together)

composition and See also:

• SPECIAL

special importance of various foods and the See also:

• LAWS

laws which regulate the See also:

• SUPPLY (through Fr. from Lat. supplere, to fill up)

supply of food under different conditions of the body are separately dealt with . Here the mode of digestion, the utilization and the elimination of the end products of the three great constituents, proteins, carbohydrates and fats, are alone considered . They are treated under the following heads: I . The See also:

• CHEMISTRY
• CHEMISTRY (formerly "chymistry"; Gr. xvµela; for derivation see ALCHEMY)

Chemistry of Digestion; II . The Mode of Formation of the See also:

• DIGESTIVE

Digestive Secretions; III . The Mechanism by which the Food is passed along the Alimentary See also:

• CANAL
• CANAL (from Lat. canalis, " channel " and " kennel " being doublets of the word)

Canal; IV . The Absorption of Food; V . See also:

• METABOLISM (from Gr. ,uera(3oXh, change)

Metabolism; VI . See also:

• EXCRETION (Lat. ex, out of, cernere, cretum, to separate)

Excretion .

1 . CHEMISTRY OF DIGESTION The essential step which prepares the See also:

• ORDINARY (med. Lat. ordinarius, Fr. ordinaire)

ordinary food for utilization in the body, for the See also:

• CHANGE (derived through the Fr. from the Late Lat. cambium, cambiare, to barter; the ultimate derivation is probably from the root which appears in the Gr. «a urmu', to bend)

change into living matter, is digestion, a See also:

• PROCESS

process which the food undergoes under the See also:

• INFLUENCE (Late Lat. influentia, from influere, to flow in)

influence of the ferments or enzymes See also:

• PRESENT

present in the gastro-intestinal See also:

• TRACT (from Lat. tractare, to treat of a matter, through Provencal tractat and Ital. trattato)

tract . By this process it is broken down into simpler substances, which can be utilized by the body tissues for See also:

• CONVERSION (Lat. conversio, from convertere, to turn or ,change)

conversion into See also:

• PROTOPLASM

protoplasm and as the supply of energy . That See also:

• PART

part which is unsuited for use in the body is either passed as faeces or absorbed and excreted in the urine . r . See also:

• ENZYME (Gr. Eve uµos, leavened, from v, in, and Om, leaven)

Enzyme See also:

• ACTION

Action generally.—The substances which bring about this change are known as ferments, enzymes or zymins . Formerly it was believed that there were two distinct classes After See also:

• BERG (Ducatus Montensis)

Berg and See also:

• SCHMIDT, H
• SCHMIDT, HEINRICH JULIAN (1818-1886)
• SCHMIDT, KARL VON (1817-1875)
• SCHMIDT, WILHELM ADOLF (1812-1887)

Schmidt . From Strasburger's Lehrbuch der Batorah, by permission of Gustav See also:

• FISCHER
• FISCHER, EMIL (1852– )
• FISCHER, ERNST KUNO BERTHOLD (1824–1907)

Fischer . g, Aril . h, See also:

• OUTER

Outer integument, interrupted at r by the raphe . m, Ruminated endosperm, n, Embryo (nat. See also:

• SIZE

size) . tica fragrans .

1 . Male See also:

• FLOWER (Lat. flos, floris; Fr. fleur)
• FLOWER, SIB

flower . 2 . See also:

• FEMALE

Female flower . is the mixed secretion from the various glands, salivary and other, the ducts of which open in the mouth . The saliva, which is for the most part produced by the three large salivary glands, the parotid, the sub-maxillary and the sub-lingual, is a See also:

• COLOUR (Lat. color, connected with celare, to hide, the root meaning, therefore, being that of a covering)

colour-less or a slightly turbid viscous fluid with a faintly alkaline reaction and of See also:

• LOW, SETH (1850- )
• LOW, WILL HICOK (1853- )

low specific gravity . It contains a very small proportion of solids, which vary somewhat in amount and See also:

• CHARACTER (Gr. xapareri7p, from xap&crew, to scratch)

character in the secretions of the different glands . Mucin and traces of other proteins are present . Small amounts of See also:

• POTASSIUM [symbol K (from kalium), atomic weight 39.114 0=16)]

potassium sulphocyanide may nearly always be detected . The functions of the saliva are twofold . First, it has a mechanical action moistening the mouth and the food and thus aiding mastication and swallowing by securing the formation of a proper bolus of food; it also assists by binding the particles together, an action of special importance when the food is dry . Second, in See also:

• MAN
• MAN, ISLE OF (anc. Mona)

man and in some of the See also:

• LOWER

lower animals the enzyme ptyalin exerts an action in digestion on part of the carbohydrates of the See also:

• DIET

diet .

The starches or polysaccharides are broken down, first of all to the See also:

• SIMPLE

simple dextrins and then to the still more simple disaccharide, maltose . The further breakdown of the maltose is carried out in the See also:

• INTESTINE (Lat. intestinus, internal, usually in neuter plural intestina. from intus, within)

intestine by the action of a ferment maltase which does not exist at all or only in the merest traces in the buccal secretion . The action of ptyalin on starches is thus very similar to that of acids, except that it stops at the formation of maltose . Ptyalin acts best at a temperature of about 4o° C. and in a neutral or faintly alkaline See also:

• MEDIUM

medium, its action being inhibited by the presence of even very dilute solutions of the See also:

• MINERAL

mineral acids . If the See also:

• ACID (from the Lat. root ac-, sharp; acere, to be sour)

acid be in sufficient amount the enzyme is destroyed . For this See also:

• REASON (Lat. ratio, through French raison)

reason the action ceases in the See also:

• STOMACH (Gr. vrbsaxos from arbga, a mouth)

stomach whenever the bolus is completely permeated by the gastric juice . As it takes See also:

• TIME (0. Eng. Lima, cf. Icel. timi, Swed. timme, hour, Dan. time; from the root also seen in " tide," properly the time of between the flow and ebb of the sea, cf. O. Eng. getidan, to happen, " even-tide," &c.; it is not directly related to Lat. tempus)
• TIME, MEASUREMENT OF
• TIME, STANDARD

time for the gastric juice thoroughly to permeate the food See also:

• MASS (O.E. maesse; Fr. messe; Ger. Messe; Ital. messa; from eccl. Lat. missa)
• MASS, IN

mass, which remains for a considerable See also:

• PERIOD
• PERIOD (Gr. irepioSos, a going or way round, circuit, aepi, round, and &Sis, way, road)

period in the fundus of the stomach unmixed with the secretion, salivary digestion goes on for about See also:

• HALF

half an See also:

• HOUR

hour after food is taken . 3 . Gastric Digestion.—The passage of food from the mouth to the stomach will be dealt with later . The stomach has two digestive functions: (1) It acts as a See also:

• STORE (from O. Fr. estor or estoire, Late Lat. staurum or instaurum, stock, provisions, supply, from the late use of instaurare, to provide, properly to construct, renew, restore)

store chamber permitting a full See also:

• MEAL

meal to be taken; (2) It acts as a digestive See also:

• ORGAN

organ of importance in preparing the food for further attack in the intestinal canal . But the stomach cannot be regarded as an essential organ, since it has been removed in See also:

• DOGS, ISLE OF

dogs and in man without apparent interference with nutrition and See also:

• HEALTH

health . Gastric digestion is brought about by the action of the gastric juice, a clear watery, colourless and strongly acid fluid with a specific gravity of about 1003 .

The amount of solids present is extremely small, about o•3 % . They consist of protein, nucleic acid, lecithin and inorganic salts, in addition to the more important constituents, the enzymes and hydrochloric acid . The amount of hydrochloric acid present in the juice varies with the period of digestion . In man the maximum acid concentration is about 0•2 % . The acid exists in the stomach in two forms as See also:

• FREE

free hydrochloric acid and as combined hydrochloric acid . The amount of each depends on various factors: (1) the secretion itself; (2) the nature of the food; and (3`) the rapidity with which the stomach empties itself, &c . For instance, after a protein-free meal the hydrochloric acid is for the most part free, whereas, when protein is present, it combines with it and, unless secreted in very large amount, most of the acid is in a fixed See also:

• CONDITION (Lat. condicio, from condicere, to agree upon, arrange; not connected with conditio, from condere, conditum, to put together)

condition . The hydrochloric acid is formed by the activities of certain gland cells in the See also:

• MIDDLE

middle region of the stomach, and the fact that it does not exist as such in the See also:

• BLOOD

blood proves that it is formed within these cells . Further, it has been found that the gastric mucous membranes of starving dogs contain 0.74 % of See also:

• SODIUM [symbol Na, from Lat. natrium; atomic weight 23.00 (0=16)]

sodium and potassium chloride, much more than is present in any other organ or in the blood plasma . That the See also:

• CHLORINE (symbol Cl, atomic weight 35`46 (0=16)

chlorine comes from the sodium chloride in the food has been shown by the fact that, when the tissues are deprived of this See also:

• SALT (a common Teutonic word, cf. Dutch zout, Ger. Salz, Scand. salt; cognate with Gr. &Xs, Lat. sal)
• SALT, SIR TITUS, BART

salt, and sodium bromide is given, hydrobromic acid may appear in the gastric tions which food comes into contact with is the saliva . This secretion . of enzymes, those which were living or associated with living cells, and those which were non-living .

In 1897, however, E . See also:

• BUCHNER, FRIEDRICH KARL CHRISTIAN LUDWIG (1824-1899)

Buchner and M . See also:

• HAHN, AUGUST (1792–1863)

Hahn showed that from living cells (yeast) a ferment could be obtained which acted quite as well extracellularly as when it was See also:

• BOUND, or BOUNDARY (from O. Fr. bonde, Med. Lat. bodena or butina, a frontier line)

bound up within the See also:

• CELL (from Lat. cella, probably from an Indo-European kal —seen in Lat. celare, to hide; another suggestion connects the word with Lat. cera, wax, taking the original meaning to refer to the honeycomb)

cell . Subsequent work has shown that other organisms See also:

• ACT (Lat. actus, actum)

act by the enzymes they contain, so that it is now recognized that there is no essential difference between the living or organized ferment and the non-living or unorganized ferment . All ferments probably act as catalysators or catalysts . See also:

• CATALYSIS (from the Gr. Kara, down, and Meta, to loosen)

Catalysis is the process by which reactions are either initiated or accelerated by the See also:

• MERE
• MERE, ADALBERT (1838-1909)

mere presence of certain substances which remain unchanged during the process; to these substances the name of catalysators has been given . As an example of such catalytic action the See also:

• ACCELERATION (from Lat. accelerare, to hasten, celer, quick)

acceleration of the decomposition of See also:

• HYDROGEN [symbol H, atomic weight x-oo8 (0=16)]

hydrogen peroxide (H202) into See also:

• WATER

water (H20) and See also:

• OXYGEN (symbol 0, atomic weight 16)

oxygen (0) by the action of a colloidal See also:

• SOLUTION (from Lat. solvere, to loosen, dissolve)

solution of See also:

• PLATINUM [symbol Pt, atomic weight 145.0 (0=16)]

platinum may be given . C . Oppenheimer defines an enzyme as a substance produced by living cells, which acts by catalysis . E . Fischer has shown that the action of ferments is specific, that is, the ferment only exerts its action on definite substances or substrates of definite structural arrangement . He has compared the relation of ferment to substrate to that of a See also:

• KEY
• KEY (in O. Eng. tang; the ultimate origin of the word is unknown; it appears only in Old Frisian kei of other Teutonic languages; until the end of the 17th century the pronunciation was kay, as in other words in O. Eng. ending in aeg; cf. daeg, day; clang
• KEY (the phraseograms being indicated by hyphens)
• KEY, SIR ASTLEY COOPER (1821-1888)
• KEY, THOMAS HEWITT (1799-1875)

key to its See also:

• LOCK (from the O. Eng. loc.; the word appears, in different forms, in many Teutonic languages, but with such various meanings as " hole," Ger. Loch, " lid," Swed. lock, &c.; probably the original was a root meaning " to enclose ")
• LOCK, MATTHIAS

lock .

Ferments which bring about the breakdown of proteins are with-out influence on fats and carbohydrates; those which decompose fats leave proteins and carbohydrates untouched, and so on . The chemical composition of enzymes is unknown . It has been assumed that they are protein in nature, but this is mainly because it has been found that when they are extracted from tissues they are apparently in See also:

• COMBINATION (Lat. combinare, to combine)

combination with proteins . In all See also:

• PROBABILITY (Lat. probabilis, probable or credible)

probability the protein is there as an impurity owing to incomplete separation . As regards the See also:

• GENERAL
• GENERAL (Lat. generalis, of or relating to a genus, kind or class)

general properties of enzymes, most of them can be precipitated from their solutions by means of See also:

• ALCOHOL

alcohol . They can also be carried down by See also:

• FINE

fine precipitates of certain inorganic salts or by protein precipitation, e.g. when a precipitate of casein is produced by acidifying a casein solution with acetic acid . Most of the ferments are soluble in water or saline solutions, and in See also:

• GLYCERIN, GLYCERINE

glycerin and water . The ferments are found to have an optimum temperature of action . This temperature in most cases ranges from 37° to 40° C . All true ferments are thermolabile, being destroyed at about 7o° C . Ferments are hindered in their action to some extent by the general protoplasmic poisons, such as salicylic acid, See also:

• CHLOROFORM (trichlor-methane), CHC13

chloroform, &c . The action of many of them is retarded when the products of their action are allowed to accumulate. just as when a chemical reaction is set up its See also:

• RATE

rate tends to decrease and finally comes to a standstill before the reaction is completed—an See also:

• EQUILIBRIUM (from the Lat. aequus, equal, and libra, a balance)

equilibrium being established—so the reactions set up by enzymes also tend to come to an equilibrium before the See also:

• COMPLETE

complete conversion of the See also:

• ORIGINAL

original substance .

In the See also:

• CASE
• CASE, JOHN (d. 1600)

case of certain enzymes at least this equilibrium may be reached from either See also:

• SIDE
• SIDE (mod. Eski Adalia)

side ; thus the enzyme maltase may either bring about the breakdown of the See also:

• SUGAR

sugar maltose to dextrose or cause a See also:

• SYNTHESIS (Gr. a6vOeacs, from avvrcBivac, to put together)

synthesis of dextrose to maltose . A number of the body ferments have now been shown to exist in the tissues in an inactive See also:

• FORM (Lat. forma)

form . This condition is known as the See also:

• PRO

pro-ferment or zymogen See also:

• STATE
• STATE, GREAT OFFICERS OF

state, and before any action can be exerted it must be activated, usually by some specific substance, as in the case of the activation of trypsinogen by means of enterokinase . The following table gives a See also:

• LIST (O.E. lisle, a Teutonic word, cf. Dut. lust, Ger. Leiste, adapted in Ital. lista and Fr. lisle)
• LIST, FRIEDRICH (1789-1846)

list of the See also:

• PRINCIPAL

principal ferments concerned in the digestion and metabolism of food-stuff s: Material acted on . Enzyme . Wh ere found . _ as_ I . Protein . . Trypsin Gastric juice II . Fats . . . Erepsin Pancreatic juice L enzymes Tissues generally ~ Lipase Pancreatic juice and Ptyalin certain tissues (salivary diastase) Saliva Pancreatic diastase Pancreatic juice Maltase Pancreatic juice Invertase Small intestine Lactase Small intestine Various See also:

• TISSUE (Fr. tissu, tissue, participle of tisser, Lat. texere, to weave)

tissue Small intestine diastases See also:

• LIVER (O. Eng. lifer; cf. cognate forms, Dutch lever, Ger. Leber, Swed. lefver, &c.; the O. H. Ger. forms are libara, lipora, &c.; the Teut. word has been connected with Gr. i'prap and Lat. jecur)

Liver, muscle, &c .

Certain oxydases, catalases and de-amidizing enzymes are found in the tissues generally and See also:

• PLAY

play an important part in the various metabolic processes . 2 . Digestion in the Mouth.—The first of the digestive secre- The hydrochloric acid is essential for the action of the gastric enzyme, See also:

• PEPSIN

pepsin, in splitting up the protein of the food . In addition to this, the acid has a slight action in splitting polysaccharides and disaccharides . Lastly, it acts as a bactericidal See also:

• AGENT (from Lat. agere, to act)

agent, preventing bacterial decomposition from taking See also:

• PLACE (through Fr. from Lat. platea, street; Gr. IrAar6s, wide)

place, and it may thus prevent certain noxious bacteria, taken in in the food, from gaining See also:

• ACCESS (Lat. accessus)

access to the intestinal tract, where there is a See also:

• CHANCE (through the O. Fr. cheance, from the Late Lat. cadentia, things happening, from cadere, to fall out, happen; cf. " case ")

chance of their flourishing in the See also:

• RICH, BARNABE (c. 1540-1617)
• RICH, CLAUDIUS JAMES (1787-1821)
• RICH, JOHN (1692-1761)
• RICH, PENELOPE, LADY (c. 1562–1607)
• RICH, RICHARD, 1ST BARON RICH (1490?-1567)

rich alkaline medium . It is owing to the presence of hydrochloric acid that gastric juice can be kept for prolonged periods without undergoing putrefaction . The quantity of juice secreted varies with the nature of the food consumed . Thus in one experiment, after the use of a test meal consisting of 25 grammes See also:

• BREAD

bread and 250 C.C. See also:

• TEA (Chinese cha, Amoy dialect t€)

tea, there was a flow of 106 c.c., whereas in another case with an ordinary meal there was an output of practically 600 c.c. gastric juice . Pawlow has shown that not only does the amount of juice secreted vary with the nature of the food ingested but that the digestive activity of the secretion also varies in the same way . He gives the following table: Quantities and Properties of Gastric Juice with Different Diets: zoo gms . Flesh, 200 gms . Bread, 600 c.c .

See also:

• MILK (0. Eng. meoluc; from a common Indo-European root, cf. Lat. mulgere, Gr. ?t dXyetv)

Milk . Hour . Quantities of Juice in c.c . Digestive See also:

• POWER [WILLIAM GRATTAN] TYRONE (1797-1841)

Power in mm . Flesh . Bread . Milk . Flesh . Bread . Milk . 1st 11.2 1o•6 4.0 4'94 6.10 4'21 and 11.3 5'4 8.6 3.03 7'97 2.35 3rd 7.6 4.0 9.2 3.01 7.51 2.35 4th 5.1 3.4 7.7 2'87 6'19 2'65 5th 2.8 3.3 4.0 3.20 5'29 6th 2.2 2.2 0.5 3.58 5.72 4.63 6.12 7th 1.2 2.6 2.25 5'48 8th o•6 2.6 3.87 5.50 .. 9th 0.9 5.75 loth o•4 rennin converts the caseinogen of the milk into paracasein, and (2) this paracasein unites with the See also:

• LIME
• LIME (O. Eng. lim, Lat. limes, mud, from linere, to smear)

lime salts present in the milk and forms the curd or precipitate .

That lime salts are absolutely essential for this process of clotting has been shown by the fact that, if they are removed by precipitation as by oxalates, no clotting will take place even after the addition of a large amount of active rennin . Immediate clotting takes place, however, when the necessary lime salts are restored . Many observers now hold that this rennet action is not the See also:

• PROPERTY

property of a specific ferment but simply another phase of the action of pepsin . For this view, which has been put forward by well-known workers, there is much to be said and certainly the power of curdling milk is not confined to the stomach, but has been found in various tissue extracts, and, indeed, wherever proteolytic enzymes are found . The See also:

• SPEED, JOHN (1552–1629)

speed with which the stomach is emptied depends to a great extent on the nature of the food . See also:

• PLAIN (O. Fr. plain, from Lat. plenum)

Plain water leaves the stomach almost at once, salt and sugar solutions at a somewhat slower rate . Milk under the action of rennin curdles . The whey rapidly leaves the stomach, whereas the casein and See also:

• FAT (O.E. fdett; the word is common to Teutonic languages, cf. Dutch vet, Ger. Fett, &c., and may be ultimately related to Greek Irian, and =apos, and Sanskrit pivan)

fat are retained for further treatment . On a mixed diet, emptying of the stomach ih man proceeds very slowly, requiring about four See also:

• HOURS, CANONICAL

hours . See also:

• CANNON (a word common to Romance languages, from the Lat. canna, a reed, tube, with the addition of the augmentative termination -on, -one)

Cannon, by feeding with food impregnated with See also:

• BISMUTH

bismuth and using X-rays, showed that carbohydrates leave most rapidly, then mixtures of carbohydrates and proteins, then proteins, then fats, and finally mixtures of fats and proteins . The diet which remains longest in the stomach is a mixture of fats and proteins-rich food, as it is popularly called . Here two factors enter to prevent rapid emptying: (1) the presence of much fat, and (2) the acid secretion engendered by the abundant protein .

There is no doubt that fats present in fine emulsion can be de-composed in the stomach . The action proceeds in a medium which is slightly acid or neutral, being entirely prevented by the presence of strong acids and alkalis . Many workers believe this gastrolipase to be of pancreatic or intestinal origin, and suppose that it gains entrance to the stomach by a reflux flow through the pylorus . See also:

• EVIDENCE (Lat. evidentia, evideri, to appear clearly)

Evidence is accumulating to show that this view is correct . By means of pepsin and gastrolipase proteins and fats are dealt with . No specific enzyme for carbohydrates has been found in the stomach in man . Certainly a small amount of polysaccharide decomposition takes place, but this is dependent (1) on the ptyalin which comes from the mouth, and (2) on a certain amount of See also:

• HYDROLYSIS (Gr. 6Swp, water, Anew, to loosen)

hydrolysis due to the action of the free hydrochloric acid . 4 . Digestion in the Intestine.-The passage of food from the stomach to the intestine will be considered later . The food so far digested in the stomach is known as chyme, and it is passed on to undergo intestinal digestion under the influence of (r) the enzymes of the See also:

• PANCREAS (Gr. rag, all; 1cpks, flesh)

pancreas, and (2) of other enzymes present in the different secretions of the intestine . Digestion in the intestine may accordingly be described under these two heads . (a) Pancreatic Digestion.-The pancreatic juice is the secretion from the pancreas and is discharged into the duodenum .

The secretion obtained from a See also:

• FISTULA (Lat. for a pipe or tube)

fistula of the pancreatic duct varies in character according to whether the opening into the duct has been made recently or some time before the examination . It is a clear, usually thin fluid with a specific gravity of about ioo8, and with an alkaline reaction . It contains a certain amount of protein and ash . The most important inorganic constituent is sodium carbonate, which gives the alkaline re-action (alkalinity is, as NaOH =o•4.7%) . This alkaline salt, along with that contained in the intestinal juice, plays an important part in neutralizing the acid chyme . In the pancreatic secretion there are at least three important enzymes, each with a definite action : (a) trypsin, the proteolytic enzyme which brings about the further breakdown of the food proteins; (b) a diastase which deals with the carbohydrates, and (c) a lipase which acts on the fats . (a) Trypsin.-This ferment, in the form in which it is secretedtrypsinogen-is inert . Before it can exert its hydrolytic action it must be activated . This activation is brought about by another enzyme which is found in the intestinal tract-enterokinase . The See also:

• CON

con-version is brought about as soon as the trypsinogen comes into con-tact with the enterokinase, the merest trace of which suffices to activate a large amount of trypsinogen . Trypsin acts on the protein just as pepsin does, by bringing about hydrolytic changes . It differs from the latter in acting best in an alkaline or neutral medium .

Its effect is much more energetic than that of pepsin, so that the protein See also:

• MOLECULE (from mod. Lat. molecula, the diminutive of moles, a mass)

molecule is more completely decomposed . Whilst it generally finishes the decomposition which the pepsin has begun, it can break down the original protein quite as easily if not more easily than does pepsin, and it carries the splitting as far as the comparatively simple crystalline bodies, the amino acids, or See also:

• GROUPS
• GROUPS, THEORY

groups of these, the polypeptides, bodies intermediate between the complex peptones and the simple amine acids of which the protein is built up . Thus each See also:

• SEPARATE

separate food gives rise to a definite hourly secretion of the juice and to a characteristic alteration in its properties . The See also:

• MEAT

meat diet brings about a very rapid flow, the maximum output taking place within the first two hours; with bread the maximum output is even earlier . With milk somewhat later . When the juice is examined as regards its digestive activity, it is found that with meat the most active juice is secreted within the first hour, with bread in the second and third hours, and with milk in the See also:

• SIXTH

sixth hour . According to the nature of the food, the stomach seems to be stimulated to form a secretion which will best serve its purpose and give the minimum of waste . It thus See also:

• WORKS

works economically . The principal ferment found in the gastric juice is pepsin, a ferment which acts only in the presence of a mineral acid . The action proceeds best at a temperature of about 37° C. in an acid medium of 0.2 % to 0.3 % . Pepsin is elaborated in the so-called See also:

• CHIEF (from Fr. chef, head, Lat. caput)

chief cells of the gastric glands as an inert precursor-propepsin . It is only when rt comes into contact with the acid of the juice that it is activated and rendered capable of attacking the protein of the food .

As already ;mentioned, the See also:

• MAIN (from the Aryan root which appears in " may " and " might," and Lat. magnus, great)
• MAIN (Lat. Moenus)

main See also:

• FUNCTION

function of the gastric juice is to See also:

• DEAL

deal with the protein moiety of the food and to prepare it for further digestion in the intestine . The first result of the action of this secretion on protein matter is to render it soluble-a metaprotein or acid See also:

• ALBUMIN, or ALBUMEN (Lat. albus, white)

albumin (syntonin), being formed . This body may be regarded mainly as the product of the action of the hydrochloric acid indepenoently of the pepsin . The following steps of decomposition are the result of the action of pepsin . From the metaprotein See also:

• PRIMARY

primary and secondary proteoses, the so-called proto-, hetero- and deutero-albumoses are formed, and prom these peptones are finally produced . The result of this process of digestion or hydrolysis induced by the pepsin is that complex protein substances of high molecular See also:

• WEIGHT

weight are converted into simpler bodies of comparatively low molecular weight . Formerly it was believed that the action of the pepsin on protein could not carry the decomposition further than the peptones, but recently it has been shown that still further splitting can be brought about, and that the simple amino acids of which the protein molecule is built up can be produced . This latter process, however, takes a very See also:

• LONG, GEORGE (1800-1879)
• LONG, JOHN DAVIS (1838– )

long time even under favourable circumstances, and it probably never occurs under normal conditions . The contents of the stomach-products of protein digestion-are passed on into the duodenum, chiefly as proteoses and peptones . In addition to the principal ferment of the gastric juice some workers hold that another enzyme is present . This is the ferment rennet, rennin, or chymosin, the See also:

• SOLE (Solea)

sole action of which, so far as is known at present, is to bring about the curdling of milk, the curd formed being dealt with in the ordinary way by the pepsin . Clotting of milk under the action of rennin occurs at a suitable temperature with great rapidity .

This process is said to take place in two stages: (i) the The character and properties of the products formed in such digestion depend on the nature of the protein acted upon . As will be seen from the following table these proteins vary fairly widely in the proportion of amino acids which they contain . moo Grammes Protein yielded Caseinogen . Gelatine . Globine Elastine . from Oxy- haemoglobine . Glycocoll 16.5 25.75 Alanine . 0.9 o•8 4'19 6.58 Leucine . I0•5 2•I 29.04 21.38 aProline . . 3'1 5.2 2.34 1.74 Phenyalanine 3.2 0.4 4'24 3'89 Glutamic acid 10.7 o•88 1.73 0.76 Aspartic acid 1.2 0.56 4'43 Cystine . . 0.065 .. 0.31 Serine 0.23 ..

0.56 Oxyproline . 0.25 3'0 1'04 Tyrosine 4'5 I'33 0.34 Lysine . . 5.8o 2.75 4'28 Histidine 2.59 0.40 10.96 .. Arginine . . 4.84 7.62 5.42 0.3 Tryptophane 1.5 .. Present Whether any of the polypeptides found in digestion are further broken down in the course of normal pancreatic digestion is a See also:

• MOOT

moot point, but E . Fischer and E . Abderhalden have shown that many of the synthetic polypeptides prepared by them can be broken into their constituents by the action of trypsin . The previous peptic digestion seems to play some part in the extent to which tryptic digestion is carried out, as one of these observers has demonstrated that protein digested first with pepsin and then with trypsin gives a smaller yield of polypeptide and a larger yield of monamino acids than when digestion has been carried out with trypsin alone . b . Diastase.-This ferment is found in the pancreatic juice apparently secreted in an active form, although some observers hold that it also is secreted in a zymogen form . It is practically identical in its action with the ptyalin of the saliva, converting See also:

• STARCH

starch into maltose .

It deals with all the starchy food which has escaped con-version into the simple sugars by the ptyalin . c . Lipase.-Most of this ferment, if not all, is apparently secreted in the form of a zymogen . There is evidence that the bile iS the activating agent here, just as the enterokinase acts in the case of trypsin . Lipase can act in any medium acid. neutral, and alkaline, and both on emulsified and non-emulsified fats . It converts the fats by a process of hydrolysis into fatty acids and glycerin . Kastle and I,oevenhart found that not only can this enzyme break up fats into their components, but that it also has the power to act in the See also:

• REVERSE

reverse direction, and in this way bring about the See also:

• UNION
• UNION (known locally as Union Hill and officially as Town of Union)

union of fatty acids and glycerin so as to form fats, a process which occurs in the intestinal See also:

• EPITHELIAL, ENDOTHELIAL

epithelial cells after absorption . In addition to these three enzymes the pancreatic juice may contain traces of others, for example, a rennet-like ferment which curdles milk . This again, as in the case of the stomach rennet, is held by some to be only another phase of proteolytic action . Maltase is also said to be present in small amount, as is also lactase under certain conditions . In pancreatic, as in gastric digestion, the nature of the food is said to play a part in controlling the amount and the composition of the secretion with respect to its ferments . The action, if it does exist, is not very well defined .

b . Intestinal Digestion.-By this is meant the other digestive processes which go on in the intestine under the action of the secretion of Lieberkiihn's follicles-the succus entericus . This is a yellowish, often opalescent, strongly alkaline fluid . The alkalinity is due to the presence of sodium carbonate . It contains a small amount of protein, See also:

• SHED

shed epithelial cells, &c . The secretion of some 170 C.C. in 24 hours has been observed in a See also:

• SHORT, FRANCIS JOB (1857– )

short See also:

• LOOP

loop of human intestine by H . S . Hamburger and E . Hekma, but it is almost impossible to get a measure of the actual amount of secretion from the whole gut . Most of the ferments are present in very small amount in the intestinal juice . They seem to be actually within the epithelial lining of the intestine, for extracts made from the intestinal mucous membrane are richer in ferments than the secretion . Apparently the intestinal secretion contains no trace of a ferment acting on native protein, but a ferment-erepsin-is present in See also:

• FAIR

fair amount in the intestinal mucous membrane and in small amount in the secretion, which acts in an alkaline medium on proteoses, peptones, and on casein, converting them into crystalline products of the nature of amino acids .

Another ferment, arginase, has been isolated from the intestinal mucous membrane by A . Kossel and H . D . Dakin, which splits the diamino acid arginin into See also:

• UREA, or CARBAMIDE, CO(NH2)2

urea and ornithin . A lipase has also beendetected which is very similar to pancreatic lipase; it, however, attacks only emulsified fats . Several See also:

• CARBOHYDRATE

carbohydrate hydrolysing enzymes have been described in the small intestine . Invertin, the ferment which splits See also:

• CANE

cane-sugar, is present in small amount in the secretion, more abundantly in the See also:

• EXTRACT (from Lat. extrahere, to draw out)

extract of mucous membrane . In all probability it deals with the saccharose after or in process of absorption . Maltase is also present in large amount, and here again in greater amount in the extract than in the secretion . The presence of lactase has been much discussed, and it seems probable that suckling animals do possess this enzyme . Some workers have stated that an intestinal diastase is to be found, but, if so, it is present in very small amount . In the large intestine a small amount of erepsin has been discovered at the upper end .

Any digestion which does take place is probably either bacterial in origin, or due to ferments which have originated in the lower end of the small intestine, and which have been carried down . 5 . Bile.-This fluid, in all probability, has little See also:

• DIRECT

direct action in ordinary digestion, although it contains substances which act indirectly . The bile salts act as solvents for fats and fatty acids, and as activators of pancreatic lipase . The salts also serve to keep cholestrin in solution . Bile is to be looked upon rather as the excretion, the result of the hepatic metabolism, than as a digestive juice . Various workers have shown that when the bile is prevented from entering the intestine owing to a fistula having been made, the See also:

• ANIMAL
• ANIMAL (Lat. animalis, from anima, breath, soul)

animal or patient may continue to enjoy See also:

• GOOD, JOHN MASON (1764-1827)

good health, thus proving that this fluid is not essential to any of the digestive processes which normally take place . Bile as secreted has an See also:

• ORANGE
• ORANGE (Citrus Aurantium)
• ORANGE, HOUSE OF

orange-See also:

• BROWN
• BROWN, CHARLES BROCKDEN (1771-181o)
• BROWN, FORD MADOX (1821-1893)
• BROWN, FRANCIS (1849- )
• BROWN, GEORGE (1818-188o)
• BROWN, HENRY KIRKE (1814-1886)
• BROWN, JACOB (1775–1828)
• BROWN, JOHN (1715–1766)
• BROWN, JOHN (1722-1787)
• BROWN, JOHN (1735–1788)
• BROWN, JOHN (1784–1858)
• BROWN, JOHN (1800-1859)
• BROWN, JOHN (1810—1882)
• BROWN, JOHN GEORGE (1831— )
• BROWN, ROBERT (1773-1858)
• BROWN, SAMUEL MORISON (1817—1856)
• BROWN, SIR GEORGE (1790-1865)
• BROWN, SIR JOHN (1816-1896)
• BROWN, SIR WILLIAM, BART
• BROWN, THOMAS (1663-1704)
• BROWN, THOMAS (1778-1820)
• BROWN, THOMAS EDWARD (1830-1897)
• BROWN, WILLIAM LAURENCE (1755–1830)

brown colour, but the colour varies according to the pigment present . It is more or less viscous (not so viscous as bile taken from the See also:

• GALL (a word common to many Teutonic languages, cf. Dutch gal, and Ger. Galle; the Indo-European root appears in Gr. xoXi,, and Lat. fel; possibly connected with " yellow," with reference to the colour of bile)
• GALL, FRANZ JOSEPH (1758-1828)

gall See also:

• BLADDER (from A.S. blaeddre, connected with bl¢wan, to blow, cf. Ger. blase)

bladder) and has a specific gravity of about Ioio . It has a slightly alkaline reaction, a See also:

• BITTER, KARL THEODORE FRANCIS (1867– )

bitter See also:

• TASTE (from Lat. taxare, to touch sharply; tangere, to touch)

taste and a characteristic See also:

• SMELL (connected etymologically with " smoulder " and " smoke ")

smell . The daily output is, for a normal individual, over 50o c.c . On See also:

• ANALYSIS (Gr. avci and Meta, to break up into parts)

analysis it is found to have over 2 % of solids, of which more than half are organic .

It contains in addition to a nucleo-albumin, derived mainly from the bile passages and gall bladder, bile acids, bile See also:

• PIGMENTS (Lat. pigmentum, from pingere, to paint)

pigments, cholesterin, lecithin, fats, &c . The most abundant solids are the salts of the bile acids, of which in man the most important is sodium glycocholate, sodium taurocholate being present in very small amount . The bile acids are formed in the liver cells, and when the duct is ligatured they tend to accumulate in the blood . The pigments amount to only about 0.2% . In human bile the chief pigment is bilirubin, whilst in herbivora biliverdin is more abundant . They are derived from the haemoglobin of the blood, but the pigments are See also:

• IRON [symbol Fe, atomic weight 55.85 (0=16)]

iron-free . They may be regarded as purely excretory products arising from the breakdown of the haemoglobin of effete blood corpuscles . Cholesterin is a monatomic alcohol, and is probably a waste pro-duct . It occurs in the bile only in small amount, and there is some evidence that it is not secreted by the liver cells but is added to the bile from the bile passages . Fats and lecithin are both derived from the liver cells . Of the inorganic constituents phosphate of See also:

• CALCIUM [symbol Ca, atomic weight 40.0 (o= x6)]

calcium is the most abundant . The secretion of bile is practically continuous, but it seems to enter the duodenum intermittently .

The taking of food increases the flow of bile, the amount of the increase depending to a certain extent on the nature of the food . A protein meal has been found to have the greatest effect and a carbohydrate one the least . The entry of the acid chyme into the duodenum is the stimulus which brings about the ejection of the bile . Pressure on the liver also seems to cause a flow (see See also:

• SECTION
• SECTION (Lat. sectio, cutting, secare, to cut)

section II.) . In connexion with bile secretion See also:

• ATTENTION (from Lat. ad-tendo, await, expect; the condition of being " stretched " or " tense ")

attention may be See also:

• DRAWN

drawn here to a See also:

• PECULIAR

peculiar enterohepatic circulation which is stated to exist . The bile salts are partly absorbed from the intestine, to be carried again by the portal blood to the liver and to be again eliminated . By this circulation the entrance of various alkaloidal and ptomaine poisons into the general circulation may be prevented . Faeces.-The bulk of the waste matter arising from the foods along with the secretions from the alimentary canal form the faeces . On an absorbable diet the faeces are almost purely intestinal in origin . As a channel of excretion of nitrogenous metabolic waste products they are not very important, although the work of C . Voit indicates that they do play a certain part . The nature of the excreted nitrogenous substances has not been fully examined .

Of the inorganic constituents iron is probably for the most part excreted into the large intestine . It is, however, very difficult to come to any definite conclusion as to what is unabsorbed material and what excreted . H . THE MODE OF FORMATION OF THE DIGESTIVE SECRETIONS r . Salivary Glands.-The secretion from the various glands is generally evoked by See also:

• NERVOUS

nervous impulses, through the secretory nerves . K . See also:

• LUDWIG, KARL FRIEDRICH WILHELM (1816—1895)
• LUDWIG, OTTO (1813-1865)

Ludwig found that the stimulation of the chorda tympani produced a copious flow of watery saliva from the submaxillary gland, and a general See also:

• DILATATION (from Lat. dis-, distributive, and lotus, wide)

dilatation of the blood-vessels supplying the gland . The same is the case in the sublingual gland . In addition to the chorda tympani See also:

• FIBRES
• FIBRES (or FIBERS, in American spelling; from Lat. fibra, apparently connected either with filum, thread, or findere, to split)

fibres also pass to the gland through the cervical sympathetic, and when these are stimulated the saliva excreted is viscous and turbid, and contains much solid matter, while the blood-vessels are contracted . The conclusion formerly drawn was that the flow of saliva was dependent on the increased blood supply . But it has been definitely proved that true secretory fibres exist . If atropine be administered before stimulation of the chorda tympani, the dilatation of the vessels takes place, but no flow of saliva .

Further, if the circulation be cut off from the gland the stimulation of the chorda tympani may cause a temporary flow of saliva . The parotid gland is supplied by the auriculo-temporal nerve which receives its secreting fibres from the glossopharyngeal . Stimulation of these fibres brings about an abundant watery secretion poor in solids . Stimulation of the sympathetic fibres See also:

• SYSTEM

system is not followed by any salivary flow, yet it has an effect on the gland, for, if after the sympathetic has been stimulated a secretion be evoked by stimulation of the glossopharyngeal nerve, the saliva secreted is very rich in organic solids . 2 . Gastric Glands.—The See also:

• CONTROL (Fr. contrdle, older form contre rolle, from Med. Lat. contra-rotulus, a counter roll or copy of a document used to check the original; there is no instance in English of the use of " control " in this, its literal, meaning)

control of the gastric secretion seems to be under two entirely different mechanisms . Pawlow has clearly shown that the stomach is supplied with secretory nerves which reach that organ through the vagus . The stimuli which bring these nerves into action are the sight, the odour or the taste of food . That the course of the stimulus is through the vagus is shown by the fact that an abundant flow of juice may be caused so long as the vagi are intact, but this flow does not take place when these nerves are cut . Between the stimulation and the secretion there is a lengthy latent time amounting to several minutes . The other stimulus of the secretion is apparently a chemical one . Pawlow states that mechanical stimulation of the mucous membrane fails to bring about a flow of juice, but See also:

• BEAUMONT
• BEAUMONT, BELMONT, or BELLOMONT
• BEAUMONT, CHRISTOPHE DE (1703-1781)
• BEAUMONT, SIR JOHN (1583–1627)

Beaumont in his classical observation on the stomach of St See also:

• MARTIN (Martinus)
• MARTIN, BON LOUIS HENRI (1810-1883)
• MARTIN, CLAUD (1735-1800)
• MARTIN, FRANCOIS XAVIER (1762-1846)
• MARTIN, HOMER DODGE (1836-1897)
• MARTIN, JOHN (1789-1854)
• MARTIN, LUTHER (1748-1826)
• MARTIN, SIR THEODORE (1816-1909)
• MARTIN, SIR WILLIAM FANSHAWE (1801–1895)
• MARTIN, ST (c. 316-400)
• MARTIN, WILLIAM (1767-1810)

Martin found that the insertion of a See also:

• TUBE (Lat. tuba)

tube did cause a flow .

There may be certain substances either present,in the food or See also:

• DEVELOPED

developed in the course of digestion, which directly stimulate the secretion originally started by a nervous reflex . E . See also:

• STARLING (0. Eng. staer steam, and slerlyng; Lat. surnus; Fr. etourneau)

Starling has drawn attention to this chemical mode of stimulating different See also:

• ORGANS

organs . To the substances known and unknown which evoke the action, he gives the name of hormones, and such " hormone " action he does not limit merely to the secretory organs but extends to all cases where one organ is stimulated by chemical products formed in the same or another organ . Attention has already been drawn to the influence of different food-stuffs on the amount and nature of the gastric secretion . 3 . Pancreatic Secretion.—The stimuli which evoke this secretion are again two in number . Many have failed to demonstrate that the secretion of the pancreas is under nervous control, but Pawlow and his school have shown that stimulation of the vagus evokes a secretion of pancreatic juice . This flow, as in the case of the stomach, has a latent period of several minutes . Most See also:

• MODERN

modern workers hold that the most effective stimulus to the pancreatic flow is the chemical one—a hormone discovered by W . Bayliss and .E . Starling, who found that extracts of the duodenal mucous membrane made with dilute hydrochloric acid when injected into the blood caused a flow of pancreatic juice .

The active substance present in this extract is known as "secretin," and is supposed to be formed under natural conditions by the action of the acid chyme on a prosecretin . This secretin is not of the ordinary zymin nature, as it is not destroyed by boiling and is soluble in alcohol . The secretin when formed must be absorbed into the blood and then carried See also:

• ROUND (O. Fr. rond, Lat. rotundus, the Fr. is the source also of Du. rond; Ger., Swed., Dan. and Nor. rond)

round the circulation to the pancreas before it can act . 4 . Intestinal Juice.—The mode of action of the stimuli which evoke this secretion has not yet been fully investigated . As has been stated, it is quite possible that very little ferment is secreted, and that ferment action mainly takes place within the cells after the various substances have been absorbed . Flow far the flow is controlled by nervous action, and how far by hormone action, is not known . Mastication.—This is a purely voluntary act, and consists of a great variety of movements rtroduced by the various muscles in connexion with the lower See also:

• JAW (Mid. Eng. jawe, jowe and geowe, O. Eng. cheowan, connected with " chaw " and " chew," and in form with " jowl ")

jaw . By the act of chewing the food is thoroughly broken up and intimately mixed with the saliva . Deglutition.—The food after thorough mastication is collected on the See also:

• SURFACE

surface of the See also:

• TONGUE (O. Eng. lunge)

tongue, principally by the action (voluntary) of the buccinator muscles, and by the contraction of the tongue muscles it is passed backwards . As soon as the food by the . action of the tongue enters the pillars of the See also:

• FAUCES (a Latin plural word for " throat "; the singular faux is rarely found)

fauces the action becomes involuntary and reflex . The soft See also:

• PALATE (Lat. palatum, possibly from the root of pascere, to feed)

palate is raised to prevent the food entering the nasal cavity, and the larynx is shut off by See also:

• CLOSURE (Fr. clooture)

closure of the glottis, and approximation of the See also:

• ARYTENOID

arytenoid cartilages to one another and to the back of the epiglottis .

The food is now passed on into the See also:

• OESOPHAGUS (Gr. o'lvca=I will carry, and r/)ayeiv, to eat)

oesophagus proper by the constrictors of the pharynx . In the oesophagus the downward See also:

• MOVEMENT

movement varies with the nature of the food swallowed . If it be fluid it reaches the lower end of the oesophagus in about three seconds and lies at the lower end of the gullet for two or three seconds before entering the stomach . When the consistency is firmer the progress downwards is much slower . Either by the force exerted by the See also:

• WAVE

wave of contraction passing down the gullet or by some See also:

• INHIBITION (from Lat. inhibere, to restrain, prevent)

inhibition of the sphincter, the cardiac orifice opens and permits the food to enter the stomach . Stomach Movements.—For our knowledge of these we are indebted principally to the work of Cannon, who studied them by feeding an animal with food containing bismuth and then following the movements of the See also:

• SHADOW (0. Eng. Schadewe, sceadu; a form of " shade "; connected with Gr. 6-Ore's, darkness)

shadow of the food on a See also:

• SCREEN (usually, but very doubtfully, connected with Lat. scrinium, a box for holding books, from scribere, to write; a connexion with Ger. Schranke, barrier, has been suggested)

screen by means of the X-rays . Soon after food is taken it is found that a contraction begins somewhere about the middle of the stomach and slowly passes towards the pylorus . This is followed by others, in man at See also:

• REGULAR

regular intervals of about twenty seconds, so that the pyloric part of the organ is soon in active peristalsis . The fundus of the stomach is not actively concerned in these movements; it simply acts as a See also:

• RESERVOIR

reservoir . At certain periods, but not with each peristaltic wave, the pyloric sphincter relaxes and allows a portion of the fluid acid chyme to See also:

• ESCAPE (in mid. Eng. eschape or escape, from the O. Fr. eschapper, modern echapper, and escaper, low Lat. escapium, from ex, out of, and cappa, cape, cloak; cf. for the sense development the Gr. iichueoOat, literally to put off one's clothes, hence to sli

escape into the duodenum . It only opens when stimulated by fluid material; if solid food be forced against it it remains tightly closed . Grutzner, by experiments with feeding with different coloured foods, has shown that the food at the fundus may remain undisturbed for quite prolonged periods .

In this connexion it must be remembered, of course, that the food is not lying loose in a See also:

• SACK

sack larger than the contents . The cavity of the stomach is only the size of the amount of food present; in other words, the food exactly fills the cavity . The motor nerve fibres to the stomach run in the vagi, which also contain fibres inhibitory to the cardiac sphincter . The splanchnic nerves mainly contain inhibitory fibres . The automatic movements are probably in connexion with the See also:

• INTRINSIC (through Fr. intrinsique, from Lat. intrinsecus, inwardly; inter, within, secus, following, from root of sequi, to follow)

intrinsic plexus of See also:

• AUERBACH, BERTHOLD (1812-1882)

Auerbach, since they continue after section of the extrinsic nerves . Intestinal Movements.—The intestines owe their peculiar movements to the arrangement of their See also:

• MUSCULAR

muscular coats, which are disposed in two layers, an inner circular, and an outer See also:

• LONGITUDINAL

longitudinal . The movements are of two kinds, the so-called swaying myogenic contraction and the peristaltic waves . The former are rapid and have very little to do with the downward movement of the contents . Probably their action is to mix the contents, since Cannon has shown that these contents, in the lower animals at least, get divided into segments . From time to time the separated segments are caught in the course of a peristaltic wave and carried downward a short distance . Then again in their new situation the rhythmic contractions break up the contents anew . The peristaltic movements are much more powerful .

Under normal conditions they begin at the pylorus and passing down-wards carry the intestinal contents onwards . The normal movement progresses slowly, although under abnormal conditions peristaltic waves may become extremely violent and rapid, and may indeed run over the whole length of the intestine within a See also:

• MINUTE
• MINUTE (Lat. minutes, small; minuere, to make less)

minute . The muscular coat in front of the contracting See also:

• ZONE (Gr. 'WV77, a girdle, from 'wvvLvay to gird)

zone is relaxed, as is that behind the wave . The waves are probably due mainly to the circular fibres, the longitudinal pulling the gut up over the contents as they are forced onwards . The downward movement seems to be due to some definite arrangement within the intestinal See also:

• WALL (O. Eng. weal, weall, Mid. Eng. wal, wane, adapted from Lat. vallum, rampart; the original O. Eng. word for a wall was wag or tenth)
• WALL, RICHARD (1694-1778)

wall, since it has been shown that, when a segment of bowel has been cut out and then the continuity of the canal made good by fixing the section so that the lower end of the excised portion is fixed to the upper divided end of the real gut, upward peristalsis takes place in this segment . An See also:

• ANTI, or CAMPA

anti-peristalsis has been described in which the movements are all towards the stomach . Under certain conditions the introduction of See also:

• FOREIGN

foreign substances, as hairs, &c., may evoke such anti-peristaltic waves . The rhythmical movements are held by some to be purely myogenic in origin, as they still continue after section of all the nerves and when the intrinsic ganglia in the intestinal wall have been thrown out of action by the application of See also:

• NICOTINE, C10H

nicotine . But See also:

• RECENT

recent work by R . See also:

• MAGNUS, HEINRICH GUSTAV (1802-1870)

Magnus would tend to show that they are controlled by Auerbach's plexus . Peristaltic waves, on the other See also:

• HAND
• HAND (a word common to Teutonic languages; cf. Ger. Hand, Goth. handus)
• HAND, FERDINAND GOTTHELF (1786-185r)

hand, according to W . Bayliss and E .

Starling, although they continue and indeed may become more energetic after section of the extrinsic nerves, are prevented by the application of nicotine and See also:

• COCAINE, C17H21NO4

cocaine; in other words, it is presumed that peristalsis is a complicated reflex action through the intrinsic ganglia . The intestines are therefore not dependent for their movement on their connexion with the central nervous system, although of course their activity is more or less regulated by such a connexion . As regards the movements of the large intestine, they resemble those of the small, although they are much less frequent . The forward movement is slow, thus permitting of the solidification of the contents by the removal of the water . In the first part of the large intestine anti-peristaltic movements are frequent, the regular peristaltic downward movements only becoming prominent when the descending See also:

• COLON
• COLON (formerly known as ASPINWALL)

colon is reached to carry contents to the rectum . The anti-peristalsis serves a useful purpose in giving time for the absorption of the fluid in the formation of faeces . The rate at which the contents travel along the intestine varies greatly . Under See also:

• AVERAGE

average conditions the food See also:

• RESIDUE (through the French, from the Lat. residuum, a remainder, from residere, to remain)

residue reaches the ileo-caecal See also:

• VALVE (Lat. valva, a leaf of a double or folding door, allied to volvere, to roll, as of a door on its hinges)

valve between the small and large intestine at about four to four and a half hours after a meal, while it takes nine hours to reach the splenic flexure of the colon . Defaecation.—Food residues, cellular debris and substances derived from the various secretions of the gastro-intestinal tract are forced downwards by peristalsis, and eventually reach the rectum and accumulate there as the faeces . The pressure of the solid and semi-solid mass gives rise to a definite sensation and a See also:

• DESIRE

desire to empty the rectum . The faeces are retained within the canal partly by the See also:

• HORIZONTAL

horizontal direction of the rectum before it opens into the anal canal, and partly by the action of two sphincter muscles . At the act of defaecation the strong See also:

• INTERNAL

internal sphincter is first of all relaxed, but unless the rectal stimulus is very strong, the See also:

• EXTERNAL

external can he kept contracted, as it is to a certain extent, under the control of the will .

The act of defaecation normally is partly voluntary and partly involuntary . The voluntary part consists in the contraction of the abdominal muscles, the closure of the glottis, and the relaxation of the external sphincter and of the levator See also:

• ANI (anc. Abnicum)

ani muscle, thus allowing the horizontal part of the rectum to become more See also:

• VERTICAL (from Lat. vertex, highest point)

vertical; the involuntary in the energetic contractions of the muscular walls of the colon and rectum which sweep the contents of the whole colon downwards . There is a centre in the lumbar enlargement of the See also:

• SPINAL

spinal See also:

• CORD (derived through the Fr. corde, from the Lat. chorda, Gr. xop(5rt, the string of a musical instrument)

cord which presides over the sphincter muscles and probably over the whole involuntary mechanism of defaecation . Vomiting.—Sometimes the gastric contents are ejected through the cardiac opening of the stomach instead of through the pylorus . The act is a reflex one, probably originally protective in nature, irritation of the gastric mucous membrane being the most frequent cause . The act is generally preceded by a feeling of See also:

• NAUSEA (from Gr. vain, a ship)

nausea and a copious salivation, succeeded by a See also:

• SERIES (a Latin word from serere, to join)

series of powerful expiratory efforts with the glottis closed . The See also:

• DIAPHRAGM (Gr. Scat/pay,aa, a partition)

diaphragm is held firmly contracted, then a convulsive contraction of the abdominal muscles with a simultaneous opening of the cardiac orifice of the stomach brings about the sudden ejection of the contents . The wall of the stomach may also See also:

• CONTRACT
• CONTRACT (Lat. contract us, from contrahere, to draw together, to bind)

contract and See also:

• PRESS (through Fr. presse from Lat. pressare, frequentative of premere, to crush, squeeze, press)

press upon the contents . During the act the glottis is firmly closed, and at the same time, if the act be not tooviolent, the gastric contents are prevented from entering the nasal cavity by the contraction of the soft palate . IV . ABSORPTION Mouth.—No absorption of food-stuffs takes place here . Stomach.—Absorption from the stomach occurs only to a small extent .

Water passes rapidly through the stomach and is practically unabsorbed . Salts are apparently absorbed in a limited amount from their watery solution, the extent of absorption depending to some extent on the concentration of the solution . Sugar is also absorbed to a small extent from its solutions, the greater the concentration the greater being the amount of sugar taken up . Alcohol is readily absorbed from the stomach . A small amount of the products of protein digestion may be absorbed: There is no evidence that fats are absorbed under any conditions in the stomach . Intestine,.—The greatest absorption of the foods takes place in the intestine, especially in the small intestine . It has been shown that over 85% of the protein has disappeared before the lower end of the small intestine is reached . How does the absorption take place ? There are two channels for the removal of the material from the intestine: (r) the blood capillaries spread in the villi, and (2) the lacteals also present in the villi . The foods may reach the blood direct or through the various See also:

• LYMPH

lymph channels into the thoracic duct and finally into the blood . The lacteals of the villi are channels for the absorption of the fatty parts of the food . The products of the digestion of the proteins and carbohydrates reach the body directly through the capillaries via the portal system .

Can absorption be explained by the ordinary laws of See also:

• DIFFUSION (from the Lat. diffundere; dis-, asunder, and fundere, to pour out)

diffusion and osmosis, or are there certain selective activities of the living epithelial lining ? The work of R . Heidenhain, E . See also:

• WEYMOUTH

Weymouth See also:

• REID, ROBERT (1862– )
• REID, SIR GEORGE (1841- )
• REID, SIR ROBERT GILLESPIE (184o-19o8)
• REID, SIR WILLIAM (1791-1858)
• REID, THOMAS (1710-1796)
• REID, THOMAS MAYNE (1818-1883)
• REID, WHITELAW (1837- )

Reid, and others shows clearly that whatever part the See also:

• PHYSICAL

physical laws play in this See also:

• EXCHANGE

exchange, there are other activities also at work . For instance, an animal's own serum can be readily absorbed from its intestine, as can also salt and other solutions of higher concentration than that of the blood . Such absorption cannot be explained by ordinary physical laws . In all such cases of absorption the epithelial lining of the gut must be intact and uninjured . O . Cohnheim and others have shown that when the epithelial lining is damaged or destroyed, the intestinal wall behaves like any other animal membrane, and the physical laws governing osmotic pressure come into play . Whether the nervous system plays any part in this absorption is not yet determined . The form in which the various products resulting from digestion are absorbed must next be considered . Carbohydrates.—These reach the body, as already mentioned, by way of the blood, and in the form of monosaccharides or simple sugars .

F . Rohmann found that the absorption of the disaccharides is dependent on the invert ferment action, and not upon their osmotic characters . E . Weinland too has shown that if lactose be put into a lactase-free intestine, no absorption takes place, the lactose gradually disappearing under bacterial action, whereas when the ferment lactase is present See also:

• GLUCOSE (from Gr. - twais, sweet)

glucose and galactose the products of its splitting are absorbed as readily as cane-sugar and maltose . E . Voit has also demonstrated the fact that the body deals with its carbohydrate supply in the form of mono-saccharides . He injected solutions of various sugars, mono- and di-saccharides, and found that the simple sugars were retained, whereas the See also:

• DOUBLE
• DOUBLE (from the Mid. Eng. duble, the form which gives the present pronunciation, through the Old Er. duble, from Lat. duplus, twice as much)

double sugars were excreted in the urine . The only di-saccharide which can be dealt with in the body is maltose, as there is a maltase present in the blood which splits it . Carbohydrates which are not absorbed from the intestine are disposed of by bacterial action, giving rise to various fatty acids, See also:

• CARBON (symbol C, atomic weight 12)

carbon dioxide, &c . Fats . -Fats are absorbed from the intestine in the form of fatty acids and glycerin; i.e. in the form in which they exist after the action of the lipase . That a resynthesis takes place in the epithelium is shown by the fact that fatty acids are of equal value with fat as a source of energy, and that as fat absorption goes on fat droplets are seen to grow in the protoplasm away from the free margin of the cells .

As already mentioned, the fat is removed by the lacteals from the cells to the thoracic duct, and then to the general circulation . A small amount of the fat may pass into the body via the blood, but this is practically all retained by the liver . The amount of fat absorbed depends a good deal on the nature of the fat, especially with reference to its melting-point, fats of low melting-point being most readily taken up . Protein.—The older workers held that the protein was absorbed in the form of proteose and peptone . In support of this it was stated that both proteoses and peptones could be detected in the blood stream . The result of the most recent work tends to show that the material is absorbed in the form of the amino acids either simple or in complex groups, the polypeptides, and that if proteoses or peptones be absorbed they are attacked by the See also:

• INTRA

intra-cellular enzyme erepsin, which breaks them down into the simpler products as soon as they are within the intestinal mucous membrane . Certain proteins appear to be absorbed unchanged; for instance, blood serum disappears from the intestine without apparently any change through zymin attack . This fact is made