FIGS  . 22, 23 and 24 from Allchin's See also:

• MANUAL

Manual of See also:

• MEDICINE

Medicine, by permission of See also:

• MACMILLAN

Macmillan & Co . Ltd . A, See also:

• PRIMARY

Primary See also:

• WAVE

wave . C, Dicrotic wave . B, Predicrotic wave . D, See also:

• POST

Post-dicrotic wave . The See also:

• FORM (Lat. forma)

form of these waves is modified by the pressure of application of the sphygmograph, and by instrumental errors; and we have no See also:

• SCALE
• SCALE (1) A

scale by which we can measure the See also:

• BLOOD

blood pressure in sphygmograph tracings . To do this another See also:

• INSTRUMENT (Lat. instrumentum, from insincere, to build up, furnish, arrange, prepare)

instrument, the sphygmomanometer, is employed . The See also:

• PULSE

pulse may pass through the arterioles and reach the capillaries when the arterioles are dilated or when the capillaries are only filled at each systole, as may be seen in the See also:

• PINK

pink of the See also:

• NAIL (O. Eng. naegal, cf. Dutch, Ger., Swed. nagel; the word is also related to Lat. unguis, Gr. ovu, Sans. nakhas)

nail when the See also:

• ARM (a common Teutonic word; the Indo-European root is ar, to join or fit; cf. the Lat. armus, shoulder, and the plural word arma, weapons, Gr. apphs, joint, and the reduplicated apapilKSV, to join)

arm is held above the See also:

• HEAD (in 0. Eng. heafad; the word is common to Teutonic languages; cf. Dutch hoofd, Ger. Haupt, generally taken to be in origin connected with Lat. caput, Gr. KerbOvi7)
• HEAD, SIR EDMUND WALKER, BART
• HEAD, SIR FRANCIS BOND, BART

head, and in cases of aortic regurgitation . A venous pulse may be recorded in the jugular vein; it exhibits oscillations synchronous with auricular and ventricular systole, and affords us important See also:

• INFORMATION (from Lat. informare, to give shape or form to, to represent, describe)

information in certain cases of See also:

• HEART
• HEART, LUNG

heart disease . The normal See also:

• AVERAGE

average pulse See also:

• RATE

rate is 72 per See also:

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

minute, in woman about 80; but individual See also:

• VARIATIONS
• VARIATIONS, CALCULUS
• VARIATIONS, CALCULUS OF

variations from 40–100 have been observed consistent with See also:

• HEALTH

health .

In the newborn the pulse beats on the average 130–140 times a minute; in a one-See also:

• YEAR

year-old See also:

• CHILD
• CHILD, FRANCIS JAMES (1825-1896)
• CHILD, L
• CHILD, LYDIA MARIA (1802-1880)
• CHILD, SIR FRANCIS (1642-1713)
• CHILD, SIR JOHN (d. 1690)
• CHILD, SIR JOSIAH (163o - 1699)

child 120–130; three years too; ten years 90; fifteen years 70-95 . Active See also:

• MUSCULAR

muscular exercise may increase the pulse rate to 130 . See also:

• NERVOUS

Nervous excitement, extreme debility and rise of See also:

• BODY

body temperature also increase it markedly . The pulse is more frequent when one stands than when one sits, or lies down, and this is especially so in states of debility . The taking of 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, especially hot food, increases it . By placing tambours on, say, the See also:

• CAROTID

carotid and radial See also:

• ARTERIES (Gr. ap-rnpia, probably from a"spew, to raise, but popularly connected by the ancients with ai7P, air)

arteries and recording the two pulses synchronously, it has been found that the pulse occurs later, the further the seat of observation is from the heart . The velocity with which the pulse wave travels down the arteries has been determined thus . It is about 7–8 metres per second . The wave length of the pulse is obtained by multiplying the duration of the inflow of blood into the aorta by the velocity of the pulse wave . It is about 3 metres . As the return of venous blood and pulmonary circulation is favoured during See also:

• INSPIRATION (Lat. inspirare, breathe upon or into)

inspiration so that the output of the See also:

• LEFT

left ventricle during the first See also:

• PART

part of inspiration is lessened and subsequently increased, From See also:

• YOUNG
• YOUNG, A
• YOUNG, ARTHUR (1741-1820)
• YOUNG, BRIGHAM (1801-1877)
• YOUNG, CHARLES MAYNE (1777–1856)
• YOUNG, EDWARD (1683–1765)
• YOUNG, JAMES (1811-1883)
• YOUNG, THOMAS (1773-1829)

Young and See also:

• ROBINSON, EDWARD (1794–1863)
• ROBINSON, HENRY CRABB (1777–1867)
• ROBINSON, JOHN (1575–1625)
• ROBINSON, JOHN (1650-1723)
• ROBINSON, JOHN THOMAS ROMNEY (1792–1882)
• ROBINSON, MARY [" Perdita "] (1758–1800)
• ROBINSON, SIR JOHN BEVERLEY, BART
• ROBINSON, SIR JOSEPH BENJAMIN (1845– )
• ROBINSON, THEODORE (1852-1896)

Robinson, See also:

• CUNNINGHAM, ALEXANDER (c.1655-173o)
• CUNNINGHAM, ALLAN (1784-1842)
• CUNNINGHAM, WILLIAM (1805-1861)

Cunningham's See also:

• TEXT (Lat. textum, woven fabric, from texere, to weave)

Text-See also:

• BOOK

Book of See also:

• ANATOMY
• ANATOMY (Gr. avaroyil, from ava-silo c', to cut up)

Anatomy . From Young and Robinson, Cunningham's Text-Book of Anatomy .

the sphygmograph reveals See also:

• RESPIRATORY

respiratory oscillations; the whole See also:

• LINE

line of the tracing falls during the first part of inspiration and rises subsequently . The circulation in the capillaries may be studied by placing under the See also:

• MICROSCOPE (Gr. µucp6s, small, asenreiv, to %view)

microscope a transparent membrane such as the See also:

• WEB (a word common to Teutonic languages, cf. Du. webbe, Dan. vaev, Ger. Gewebe, all from the Teutonic wabh—to weave)

web of the The See also:

• FROG

frog's See also:

• FOOT

foot, tail of See also:

• TADPOLE

tadpole, wing of See also:

• BAT

bat, &c . By a See also:

• SPECIAL

special capillary See also:

• ILLUMINATION

illumination one may see the See also:

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

shadow of the blood See also:

• COR

cor- cacula- puscles moving through the retinal vessels of one's own See also:

• EYE
• EYE (O. Eng. edge, Ger. Auge; derived from an Indo-European root also seen in Lat. oc-ulus, the organ of vision (q.v.)

eye, See also:

• DON
• DON (anc. Tanais)

don. and even calculate the velocity of flow . The See also:

• DIAMETER (from the Cr. &a, through, µErpov, measure)

diameter of the smaller capillaries is such as to permit the passage of the red blood corpuscles in single See also:

• FILE

file only; their length is about nth of an See also:

• INCH (O. Eng. ynce from Lat. uncia, a twelfthpart; cf. " ounce," and see As)

inch . The endothelial cells confine the blood from See also:

• DIRECT

direct contact with the See also:

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

tissue See also:

• LYMPH

lymph and so prevent its coagulation, but allow and regulate the See also:

• EXCHANGE

exchange of material between the blood and lymph . This exchange is regulated by the vital activity of the cells, and does not follow such See also:

• LAWS

laws as pertain to filtration and See also:

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

diffusion through dead membranes . There is See also:

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

evidence to show that the cells of the hepatic capillaries are capable of protoplasmic See also:

• MOVEMENT

movement and of See also:

• PHAGOCYTOSIS (Gr. 0ayeiv, to eat, devour, and KtTOS, cell)

phagocytosis . The pressure in the capillaries stands in closer relationship to that in the See also:

• VEINS

veins than to that in the arteries; for example, a rise of pressure in the venae cavae, other things remaining the same, raises the pressure in the hepatic capillaries to a like amount, while a rise of pressure in the aorta does not, for most of the arterial pressure is spent in overcoming the peripheral resistance . The filling of the capillaries in the skin varies greatly with temperature, posture, &c . When the See also:

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

hand is See also:

• COLD (in O. Eng. cald and ceald, a word coming ultimately from a root cognate with the Lat. gelu, gelidus, and common in the Teutonic languages, which usually have two distinct forms for the substantive and the adjective, cf. Ger. Kolte, kalt, Dutch koude

cold the arterioles are so constricted that blood only passes through the wider and more direct capillaries . As the skin becomes warm it flushes, the arterioles dilating and all the capillary networks becoming filled with blood . Muscular movements See also:

• EXPRESS (through the French from the past participle of the Lat. exprimere, to press out, by transference used of representing objects in painting or sculpture, or of thoughts, &c. in words)

express the blood out of the capillaries, as may be seen by the blanching of the skin which occurs on clenching the hand .

Raising the hand blanches, and lowering it congests the capillaries . The pressure and velocity in the capillaries thus constantly vary, owing to alterations in hydrostatic pressure, the pressure of the body against See also:

• EXTERNAL

external See also:

• OBJECTS

objects, the contraction of the muscles, and the contraction of the arterioles . It is not possible therefore to set any definite figure to the capillary pressure or velocity . In the frog's web, with the foot confined and at See also:

• REST (O. Eng. rest, reste, bed, cognate with other Teutonic forms, e.g. Ger. Rast, Riiste, rest, and probably Gothic Rasta, league, i.e. resting or stopping place)

rest, the velocity is about t mm. per second . We continually make slight movements to counteract the hydrostatic effect and prevent the congestion of blood in the capillaries of See also:

• LOWER

lower parts of the body . It is this tendency to congestion which makes it so difficult to stand absolutely See also:

• MOTION (Lat. motio, from movere, to move)
• MOTION, LAWS OF

motion-less for any length of 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 . The red corpuscles, being the heavier, occupy the See also:

• AXIS (Lat. for " axle ")

axis, and the See also:

• WHITE
• WHITE, ANDREW DICKSON (1832– )
• WHITE, GILBERT (1720–1793)
• WHITE, HENRY KIRKE (1785-1806)
• WHITE, HUGH LAWSON (1773-1840)
• WHITE, JOSEPH BLANCO (1775-1841)
• WHITE, RICHARD GRANT (1822-1885)
• WHITE, ROBERT (1645-1704)
• WHITE, SIR GEORGE STUART (1835– )
• WHITE, SIR THOMAS (1492-1567)
• WHITE, SIR WILLIAM ARTHUR (1824--1891)
• WHITE, SIR WILLIAM HENRY (1845– )
• WHITE, THOMAS (1628-1698)
• WHITE, THOMAS (c. 1550-1624)

white corpuscles the peripheral layer of the capillary stream . If an irritant is placed on the membrane it will be observed that the capillaries become wider and crowded with corpuscles, the flow slackening and finally becoming arrested owing to the passing out of the plasma through the damaged capillary 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 . The white corpuscles creep out between the endothelial cells into the tissues . Such are the first phenomena of inflammation . After obstruction of an artery See also:

• COLLATERAL (from Med. Lat. collateralis,—cum, with, and latus, lateris, side,—side by side, hence parallel or additional)

collateral pathways are in most parts rapidly formed, for the anastomatic capillaries, stimulated by the increased blood flow, develop into arterioles and arteries . Numerous anastomoses exist between the veins, so that if the flow of blood be obstructed in one direction it readily finds a passage The flow in another .

Muscular movement, alterations of posture and la the respiratory movements particularly forward the venous veins. circulation . The See also:

• BARBER (from Lat. barba, beard)

barber's See also:

• POLE (FAMILY)
• POLE, REGINALD (1500-1558)
• POLE, RICHARD DE LA (d. 1525)
• POLE, WILLIAM (1814—1900)

pole of the barber surgeon was grasped to increase the flow in the old blood-letting days . The valves in the veins allow the blood to be forced only towards the heart . The pressure in the veins varies according to the hydrostatic pressure of the blood See also:

• COLUMN (Lat. columna)

column above the point of measurement . In the See also:

• HORIZONTAL

horizontal position, when this See also:

• FACTOR (from Lat. facere, to make or do)

factor is almost eliminated, the pressure in the large veins is about equal to 5–Jo mm. of See also:

• MERCURY
• MERCURY (MERCU1uus)
• MERCURY (symbol Hg, atomic weight = 2oo)

mercury, and even may become negative on taking a deep inspiration . There thus arises the danger of See also:

• AIR (from an Indo-European root meaning " breathe," " blow ")
• AIR, or ASBEN

air being sucked into a wounded jugular vein . If air does thus gain entry it may fatally obstruct the circulation . The venous circulation is impeded by (i) a lessening of heart See also:

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

power, (2) valvular defects, such as incompetence or narrowing of the orifice which they guard, (3) obstruction to the filling of the heart, as in cases of pericardial effusion, (4) obstruction of the pulmonary circulation as in coughing, by pleuritic effusion, &c . The results of venous congestion are a less efficient arterial circulation, a dusky See also:

• APPEARANCE (from Lat. apparere, to appear)

appearance of the skin, a fall of cutaneous temperature, and an effusion of fluid into the tissue spaces producing oedema and See also:

• DROPSY (contracted from the old word hydropisy, derived from the Gr. 154w¢; i Swp, water, and appearance)

dropsy . This last effect is not due to increased capillary pressure producing increased transudation as has been supposed, for no such increase in venous and capillary pressure persists under the conditions . It is due to the altered See also:

• NUTRITION

nutrition of the capillary endothelium and the tissues, which results front the deficient circulation . If for any See also:

• REASON (Lat. ratio, through French raison)

reason the left ventricle fail to maintain its full systolic output, it ceases to receive the full auricular input, and in consequence the pulmonary vessels congest .

This tells back on the right heart, and the right ventricle is unable to empty itself into the congested pulmonary vessels, and this in its turn leads to venous congestion . The final result of any obstruction thus is a pooling of the blood in the venous cistern . Dyspnoea results from cardiac insufficiency . It is excited by the increased venosity of the blood acting on the respiratory centre . Both excess of See also:

• CARBON (symbol C, atomic weight 12)

carbon dioxide and deficiency of See also:

• OXYGEN (symbol 0, atomic weight 16)

oxygen excite this centre . The increased respiratory movements aid the circulation . The venous See also:

• SIDE
• SIDE (mod. Eski Adalia)

side of the vascular See also:

• SYSTEM

system, owing to the See also:

• GREAT

great See also:

• SIZE

size of the veins, has a large potential capacity, while many of the capillaries in each See also:

• ORGAN

organ are empty and collapsed, except at those periods of vaso-See also:

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

dilatation and hyperaemia which accompany extreme activity of See also:

• FUNCTION

function . The vascular system cannot be regarded as a closed system, for the blood-plasma, ,whenever the capillary pressure is increased, transudes through the capillary wall into the tissue-spaces and enters the lymphatics . Thus, if fluid be transfused into the circulatory system, it not only collects in the capacious reservoirs of the veins and capillaries—especially in the lungs, 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 and abdominal See also:

• ORGANS

organs–but leaks into the tissue-spaces . Hence the pressure in the vascular system cannot be raised above the normal for any length of time by the injection of even enormous quantities of fluid . The lymphatics of tissue-spaces must be regarded as part of the vascular system . There is a See also:

• CONSTANT, BENJAMIN (1845-1902)

constant give and take between the blood-plasma and the tissue lymph .

If the fluid part of the blood be increased, then the capillary transudation becomes greater, and the excess of fluid is excreted from the kidneys and glands of the alimentary See also:

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

canal . If the fluid part of the blood diminish, then fluid passes from the tissue-spaces into the yaemor- blood, and the sensation of thirst arises, and more drink is rh~e and taken . The circulation may be greatly aided by the trans-. See also:

• FUSION

fusion of 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 See also:

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

solution (0.8 %) or blood after severe hemor- See also:

• SION [Ger. Sitten]

sion . rhage, or in states of surgical See also:

• SHOCK, or COLLAPSE

shock . Only the blood of See also:

• MAN
• MAN, ISLE OF (anc. Mona)

man must be used . The direct giving of blood by connecting the radial artery of a relation to the median vein of a patient has been used as a means of effecting restoration . Blood may be withdrawn from the system slowly to the extent of 4 %, rapidly to the extent of 2 % of the bodyweight, without lowering the arterial pressure, owing to the compensatory contraction of the arterioles and the rapid absorption of fluid from the tissues into the blood . The withdrawal of the tissue-lymph excites extreme thirst and the great need for See also:

• WATER

water which occurs after severe hemorrhage . About 75 % by See also:

• WEIGHT

weight of the tissues, excluding 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 and See also:

• BONE (a word common in various forms to Teutonic languages, in many of which it is confined to the shank of the leg, as in the German Bein)
• BONE, HENRY (1755-1834)

bone, consists of water . The quantity of blood in the body is about Q~th of the body weight . That of tissue-lymph is unknown, but it must be considerable, probably greater than that of the blood; The lymphatics drain off the excess of fluid which transudes from the capillaries, and finally return it to the vascular system . The interchange between tissue, blood and lymph depehds on the forces of the living cells, which are as yet far from See also:

• COMPLETE

complete elucidation .

We may define the velocity of the blood at any point in a See also:

• VESSEL (O. Fr. vaissel, from a rare Lat. vascellum, dim. of vas, vase, urn)

vessel as the length of the column of blood flowing by that point in' second . In the See also:

• CASE
• CASE, JOHN (d. 1600)

case of a See also:

• TUBE (Lat. tuba)

tube, supplied by a constant head of pressure, we can See also:

• DIVIDE

divide the tube and measure velocity the outflow per second; knowing the See also:

• VOLUME

volume of this, oTf blood and the See also:

• CROSS

cross See also:

• AREA

area of the artery, we can determine the length of the column . This See also:

• KIND (O. E. ge-cynde, from the same root as is seen in " kin," supra)

kind of experiment flow. cannot be done on the living See also:

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

animal, because the opening of the vessel alters the resistance to flow, and the loss of blood also changes the physiological conditions . To determine the velocity other means must be devised . See also:

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

Ludwig invented an instrument called the stromuhr, consisting of two bulbs mounted on a rotating See also:

• PLATFORM (Fr. plateforme, i.e. ground plan)

platform pierced with two holes . One bulb is filled with oil—the other with blood . The bulbs are connected together by a tube at their upper end, and the lower end of the one full of oil is brought over the hole in the platform . The central end of the artery is connected to the same hole and the peripheral end to the other, over which stands the bulb full of blood . The blood being allowed to flow displaces the oil out of the one bulb into the other; directly this happens, the bulbs are rotated and the one full of oil is again brought over the central end of the artery . The number of rotations per minute is counted, and the volume of the bulb being known we obtain the volume of blood that passes through the instrument per a - minute . In another instrument, the haemo- c dromograph of Chauveau, there is inserted FIG . 25.-Ludwig', into the artery al tube in which hangs a small Stromuhr. pendulum; the See also:

• STEM (O. Eng. staefn, stemn, cf. Du. stain, Ger. Stamm, &c., probably related to " staff ")

stem of the pendulum passing through a See also:

• RUBBER, INDIARUBBER

rubber See also:

• DAM

dam which closes the See also:

• VERTICAL (from Lat. vertex, highest point)

vertical See also:

• LIMB

limb of the tube .

The pendulum is deflected by the flow, and the greater the velocity the greater the deflection . The deflection can be recorded by connecting the See also:

• FREE

free end of the pendulum to a See also:

• TAMBOUR (Fr. for " drum " )

tambour arrangement . This instrument allows us to See also:

• RECORD (Lat. recordari, to recall to mind, from cor, heart or mind)

record and measure the variations of velocity during systole and diastole of the heart, but it can only be used in the vessels of large animals . Still other methods have been employed by Cybuleki and See also:

• STEWART, ALEXANDER TURNEY (1803-1876)
• STEWART, BALFOUR (1828-1887)
• STEWART, CHARLES (1778–1869)
• STEWART, DUGALD (1753-1828)
• STEWART, J
• STEWART, JOHN (1749—1822)
• STEWART, JULIUS L
• STEWART, SIR DONALD MARTIN (1824–19o0)
• STEWART, SIR HERBERT (1843—1885)
• STEWART, SIR WILLIAM (c. 1540—c. 1605)
• STEWART, STUART
• STEWART, WILLIAM (c. 1480-c. 1550)

Stewart . The See also:

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

general relations of the velocity of the blood in the arteries, capillaries and veins is expressed by the See also:

• CURVE (Lat. curvus, bent)

curve shown in fig . 26 . The velocity in the large arteries may reach 50o mm. per second in systole and fall to 15o mm. in diastole . The smaller the artery I The introduction of rubber tubing for the connexions made the the less is this difference and the more See also:

• UNIFORM

uniform the rate of flow, method. of inquiry comparatively See also:

• SIMPLE

simple . The tubing connecting the arterial cannula and the See also:

• MANOMETER (Gr. µavos, thin or loose; µerpov, a measure)

manometer was filled with a suitable fluid to prevent coagulation of the blood; also to prevent more than a trace of blood entering the connexions . A saturated solution of See also:

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

sodium sulphate, or a i % solution of sodium citrate, may be employed for this purpose . Ludwig (1847) added a See also:

• FLOAT (in O. Eng. floc and flota, in the verbal form f eotan; the Teutonic root is flut-, another form of flu-, seen in " flow," cf. " fleet "; the root is seen in Gr. a-M e, to sail, Lat. pluere, to rain; the Lat, fluere and fluctus, wave, is not connect

float provided 1; ; 1 with a See also:

• WRITING
• WRITING (the verbal noun of " to write," O. Eng. writan, to inscribe)

writing See also:

• STYLE
• STYLE (from Gr. a-6'1ms, a column; a different word from that used in literature, see below)

style to the See also:

• MERCURIAL

mercurial manometer, and brought the style to write on a See also:

• DRUM (early forms drome or dromme, a word common to many Teut. languages, cf. Dan. tromme, Ger. Trommel: the word is ultimately the same as " trumpet," and is probably onomatopoeic in origin; it appears late in Eng. about the middle of the 16th century)

drum covered with smoked See also:

• PAPER
• PAPER (Fr. papier, from Lat. papyrus)

paper and driven slowly See also:

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

round by clockwork—a kymograph By this means tracings of the arterial blood pressure are obtained, and the See also:

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

influence upon the blood pressure of various agents recorded and studied . For the veins a manometer filled with salt solution is used, as mercury is too heavy a fluid to record the far slighter changes of venous pressure .

The manometer may be connected with a recording n Je`~> tambour . The arterial blood-pressure record obtained with the mercurial manometer exhibits cardiac and respiratory oscillations as shown ' lreiha in fig . 18 . The method gives us a fairly accu- • rate record of the mean pressure, but the See also:

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

mass of the mercury causes such inertia that the instrument is quite unable to faithfully record the systolic and diastolic variations of pressure . To effect this record, delicate See also:

• SPRING (from " to spring," " to leap or jump up," " burst out," O. Eng., springau, a common Teut. word, cf. Ger. springer, possibly allied to Gr. QnrFpxecOac, to move rapidly)

spring manometers of rapid See also:

• ACTION

action and small inertia have been in-vented . A mercury manometer provided with maximum and minimum valves has also been employed to indicate the maximal systolic and minimal diastolic pressure . To determine the blood pressure in man, an instrument called the sphygmometer is used . The writer's sphygmometer consists of a rubber bag covered with d See also:

• SILK

silk which is filled with air, and See also:

• CON

con- nected by a See also:

• SHORT, FRANCIS JOB (1857– )

short length of tube to a manometer . This manometer con- sists of a graduated See also:

• GLASS
• GLASS (O.E. glees, cf. Ger. Glas, perhaps derived from an old Teutonic root gla-, a variant of glo-, having the general sense of shining, cf. " glare," " glow ")
• GLASS, STAINED

glass tube, open at one end . A small hole is in the side of the tube near this end . A r,.r may meniscus of water is introduced up to the side hole—the zero See also:

• MARK
• MARK, CARL (1858– )
• MARK, GOSPEL OF ST
• MARK, ST

mark on the scale—by placing the open end of the i tube in water . The bag is now con- nected 1 to the See also:

• GAUGE, or GAGE (Med. Lat. gauja, jaugia, Fr. jauge, perhaps connected with Fr. jale, a bowl, galon, gallon)

gauge so that the side hole is closed by the rubber tube .

Covering the rubber bag with the hand and pressing it on the radial artery until the pulse (See also:

• FELT (cognate with Ger. Filz, Du. vilt, Swed. and Dan. fill; the root is unknown; the word has given Med. Lat. filtrum, " filter ")

felt beyond) is obliter- ated, one reads the height to which i the meniscus rises in the manometer, and this gives us the systolic pressure in the artery . The air above the meniscus acts as a spring, converting the instrument into a spring manometer . It is empirically graduated in mm . Hg. r It is very necessary to remember that the blood pressures, taken in different vessels and postures, vary with the hydrostatic pressure of the column of blood above the point of measure- ment . (t, Thus in the See also:

• STANDING

standing posture the arterial pressure in the arteries of the See also:

• LEG
• LEG (a word of Scandinavian origin, from the Old Norwegian leggr, cf. Swed. lagg, Dan. laeg; the O. Eng. word was sceanca, shank)

leg is higher than in the arm by the height of the column of blood that separates the two points of measure- ment . In the horizontal posture the pressure is practically the same in all the big arteries . The pressure in the ascending aorta is kept about the same in all postures, while that of the leg arteries varies widely . The effect of gravity is compensated there by active changes in heart force, splanchnic dilatation, &c . (L . See also:

• HILL
• HILL (0. Eng. hyll; cf. Low Ger. hull, Mid. Dutch hul, allied to Lat. celsus, high, collis, hill, &c.)
• HILL, A
• HILL, AARON (1685-175o)
• HILL, AMBROSE POWELL
• HILL, DANIEL HARVEY (1821-1889)
• HILL, DAVID BENNETT (1843–1910)
• HILL, GEORGE BIRKBECK NORMAN (1835-1903)
• HILL, JAMES J
• HILL, JOHN (c. 1716-1775)
• HILL, MATTHEW DAVENPORT (1792-1872)
• HILL, OCTAVIA (1838– )
• HILL, ROWLAND (1744–1833)
• HILL, SIR ROWLAND (1795-1879)

Hill) . The systolic pressure of young men, taken in the radial artery with the arm at the same level as the heart, may be taken to be about See also:

• ITO, HIROBUMI, PRINCE (1841-1909)

Ito mm. of Hg . In men of 4o-6o years the systolic pressure is often about 140 mm., but in some robust men it is no higher than in youth .

The venous pressure in man may be measured by finding the pressure just required to prevent a cutaneous vein refilling after it has been emptied beyond a 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 . There is no accurate method The time necessary for a See also:

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

section of the system . Thus the greatest velocity is where the See also:

• TOTAL

total See also:

• BED
• BED (a common Teutonic word, cf. German Bett, probably connected with the Indo-European root bhodh, seen in the Lat. fodere, to dig; so " a dug-out place " for safe resting, or in the same sense as a garden " bed ")

bed is narrowest, and slowest where the bed widens to the dimensions of a See also:

• LAKE
• LAKE, GERARD LAKE, 1ST VISCOUNT (1744-1808)

lake . The blood in leaving the heart may take a short See also:

• CIRCUIT (Lat. circuitus, from circum, round, and ire, to go)

circuit through the coronary system of the heart and so back to the right heart, or it may take a See also:

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

long an devious course tothe toes and back, or through the intestinal capillaries, portal system and hepatic capillaries . It is obvious, then, that the time any two particles of blood take to complete the circuit may be widely different . Experiments have been made to determine how rapidly any substance, like a See also:

• POISON

poison, which enters the blood ma be distributed over the body . A salt such as See also:

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

potassium ferrocyanide is injected into the jugular vein, and the blood collected• in successive samples at seconds of time from the opposite jugular vein . These samples are tested for the presence of the salt, or a strong solution of methylene See also:

• BLUE (common in different forms to most European languages)

blue is injected into the jugular vein, and the moment determined with a stop-See also:

• WATCH (in O. Eng. wcecce, a keeping guard or watching, from wacian, to guard, watch, wacan, to wake)

watch when the blue See also:

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

colour appears in the carotid artery . The velocity of flow also can be determined in any organ by injecting salt solution into an artery, and observing, with the aid of a See also:

• WHEATSTONE, SIR CHARLES (1802–1875)

Wheatstone's See also:

• BRIDGE

bridge arrangement, the galvanometric 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 in See also:

• ELECTRICAL
• ELECTRICAL (or ELECTROSTATIC) MACHINE

electrical resistance which occurs in the corresponding vein when the salt solution reaches it . The moment of injection and that of the alteration in resistance are observed with a stop-watch (Stewart) . It has been determined that the blood travelling fastest can complete the circuit in about the time occupied by 25 to 30 heart-beats, say in 20 to 30 seconds; a result which shows how rapidly methods must be taken to prevent the absorption of poisons—for example, snake-poison . The blood travelling fastest in the pulmonary circuit occupies only about one-fifth of the time spent by that in the systemic circuit .

That some of the blood takes a very long time to return to the heart is shown by the long time it takes to See also:

• WASH, THE

wash the vascular system free of blood by the injection of salt solution . That the blood is under different pressure in the various parts of the The system has long been known . From a divided artery the pressure blood flows out in forcible spurts, while from a vein it relation flows out continuously and with little force . It takes in the very little pressure of the fingers to blanch the capillaries vascular of the skin, but an appreciable amount to obliterate the system. radial artery . Flo . 28.—Hill's Sphyg- Capillaries .. From Allchin's Manual of Medicine, by permission of Macmillan & Co . Ltd . , complete circula- tion . Arteries the Blood in the Arteries, Capillaries and Veins . The flow in the large veins is approximately equal to that in the large arteries . In the jugular vein of a See also:

• DOG

dog the mean velocity was found to be 225 mm. and in the carotid 260 mm. per second .

The velocity in the capillaries has been measured by direct observation with the microscope . It is very small, e.g. o .5-I mm. per second . The variation of velocity in different parts of the vascular system is explained by the difference in width of bed through which the stream flows . The vascular system may be compared to a stream which on entering a See also:

• FIELD (a word common to many West German languages, cf. Ger. Feld, Dutch veld, possibly cognate with O.E. f olde, the earth, and ultimately with root of the Gr. irAaror, broad)
• FIELD, CYRUS WEST (1819-1892)
• FIELD, DAVID DUDLEY (18o5-1894)
• FIELD, EUGENE (1850-1895)
• FIELD, FREDERICK (18o1—1885)
• FIELD, HENRY MARTYN (1822-1907)
• FIELD, JOHN (1782—1837)
• FIELD, MARSHALL (183 1906)
• FIELD, NATHAN (1587—1633)
• FIELD, STEPHEN JOHNSON (1816-1899)
• FIELD, WILLIAM VENTRIS FIELD, BARON (1813-1907)

field is led into a multitude of See also:

• IRRIGATION (Lat. in, and rigare, to water or wet)

irrigation channels, the sum of the cross sections of all the channels being far greater than that of the stream . The channels unite together again and leave the field as one stream . If the flow proceeds uniformly for any given unit of time, the same volume must flow through any cross See also:

• STEPHEN
• STEPHEN (1097?-1154)
• STEPHEN (ISTVAN) BATHORY (1533-1586)
• STEPHEN, SIR JAMES (1789-1859)
• STEPHEN, SIR JAMES FITZJAMES, BART
• STEPHEN, SIR LESLIE (1832-1904)

Stephen See also:

• HALES, JOHN (1584-1656)
• HALES, or HAYLES, JOHN (d. 1571)
• HALES, STEPHEN (1677-1761)

Hales (1733) was the first to measure the blood pressure . He inserted a See also:

• BRASS
• BRASS (O. Eng. braes)

brass tube into the femoral vein of a See also:

• HORSE (a word common to Teutonic languages in such forms as hors, hros, ros; cf. the Ger. ross)

horse and connected it to a long glass tube held vertically, using the trachea of a See also:

• GOOSE (a common Teut. word, O. Eng. gOs, pl. ges, Ger. Gans, O. Norse gas, from Aryan root, ghans, whence Sans. hansa, Lat. anser (for hanser)
• GOOSE (GAME OF)

goose as a flexible tube, and found the blood See also:

• ROSE
• ROSE (Rosa)
• ROSE, GEORGE (1744-1818)
• ROSE, HUGH JAMES (1795—1838)
• ROSE, WILLIAM STEWART (1775-1843)

rose to the height of 8 ft., oscillated there with each heart-See also:

• BEAT (a word common in various forms to the Teutonic languages; it is connected with the similar Romanic words derived from the Late Lat. battere)

beat, and rose and See also:

• FELL
• FELL, JOHN (1625-1686)

fell some-what with inspiration and expiration . In the vein he found the pressure to be only about 12 in . Poiseuille (1828) adapted to the same purpose the mercurial manometer, a U-shaped tube containing mercury, which, being 13.5 times heavier than blood, allowed the manometer to be brought to a convenient height . mometer . From See also:

• HOWELL, JAMES (c. 1594-1666)

Howell's Text-Book of See also:

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

Physiology, by permission of W . B .

Saunders Co . and Diastolic Pressure . Systolic or nl xtmuof ro i mm zoo mm Mean `WA~ . _- WAIL Diastolic or minimum 8omm See also:

• BASE

Base line -6o mm -4o mm -somm it is difficult to determine whether a rise of pressure in the pulmonary artery is induced really by constriction of the pulmonary system, or by changes in the output of the heart; hence different observers have reached conflicting conclusions . In the case of lungs which have been supplied with an artificial circulation and a constant head of pressure to eliminate the action of the heart, no diminution in outflow has been observed in exciting the branches of the vagus or sympathetic nerves which See also:

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

supply the lungs, or by the injection of adrenalin (See also:

• SIR

Sir See also:

• BENJAMIN
• BENJAMIN, JUDAHPHILIP (1811-1884)

Benjamin C . See also:

• BRODIE, PETER BELLINGER (1815–1897)
• BRODIE, SIR BENJAMIN COLLINS

Brodie (1783–1862), and See also:

• DIXON
• DIXON, GEORGE (1755 ?–1800)
• DIXON, HENRY HALL (1822-1870)
• DIXON, RICHARD WATSON (1833-1900)
• DIXON, WILLIAM HEPWORTH (1821-1879)

Dixon, See also:

• BURTON, JOHN HILL (1809–1881)
• BURTON, ROBERT (1577-1640)
• BURTON, SIR FREDERICK WILLIAM (1816–f goo)
• BURTON, SIR RICHARD FRANCIS (1821-1890)
• BURTON, WILLIAM EVANS (1804-1860)

Burton-Spitz) . The portal circulation is See also:

• PECULIAR

peculiar in that the blood passes through two sets of capillaries . Arterial blood is conveyed to the capillary networks of the See also:

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

stomach, See also:

• SPLEEN (Gr. o-1rXilv)

spleen, See also:

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

pancreas and intestines The by branches of the abdominal aorta The portal vein is of measuring the capillary pressure . It and the venous pressure constantly vary from nothing to a See also:

• POSITIVE (or PORTABLE) ORGAN

positive amount with rest or movement of muscles, change of posture, &c . The arterial pressure is raised during exertion by the more forcible beat of the heart—e.g. pressures of 140–190 mm . Hg have been observed immediately after a 3-mile See also:

• RACE

race . It rapidly sinks to a lower level than usual after the exertion is over, e.g .

90 mm . Hg, owing to the quieter action of the heart and the persistence of the cutaneous dilatation of the blood vessels which is evoked by the rise of body temperature . The writer has observed in athletes rectal temperatures of 102–105° F. after long races . After meals there is an increase in cardiac force to maintain the flow through the dilated splanchnic vessels . See also:

• MENTAL

Mental excitement raises the pressure—e.g. the writer's pressure may be to mm. before and 125 mm . Hg after giving a lecture . The origin of the blood pressure in the arteries is the See also:

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

energy of the heart . The pressure gradient depends on the peripheral resistance . In the arterials the pressure is spent, and little of it reaches the capillaries . The return of the capillary blood to the veins and the pressure in the veins is due partly to the See also:

• REMAINDER, REVERSION

remainder of the cardiac force, but more largely to the contraction of the skeletal muscles and the viscera, to the action of gravity in changes of posture and to the respiratory See also:

• PUMP

pump . The pulmonary artery, carrying venous blood, divides and sub- divides, and the smallest branches end in a plexus of capillaries The pul- on the walls of the air-cells of the See also:

• LUNG

lung . From this plexus the blood is drained by the radicles of the four pulmonary monary veins which open into the left See also:

• AURICLE (from Lat. diminutive of auris, ear)

auricle .

The pressure in c/rcu/a- the pulmonary artery is less than one-third the aortic uO°' pressure, and the blood takes only one-third of the time to complete the pulmonary circuit that it takes to make the systemic . The four See also:

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

chief factors which influence the pulmonary circulation are: (1) the force and output of the right ventricle; (2) the diastolic filling action of the left auricle and ventricle; (3) the diameter of the pulmonary capillaries, which varies with the respiratory expansion of the lungs; (4) the intrathoracic pressure . In inspiration the lungs are distended in consequence of the greater positive pressure on the inner surfaces being greater than the negative pressure on their See also:

• OUTER

outer pleural surfaces . The negative pressure in the intrathoracic cavity results from the enlargement of the See also:

• THORAX (Gr. BWpaE, breastplate, also the part of the body covered by it)

thorax by the inspiratory muscles . When the elastic lungs are distended by a full inspiration they exert an elastic See also:

• TRACTION (Lat. trahere, to draw)

traction amounting to about 15 mm . Hg . The heart and vessels within the thorax are submitted to this traction—that is, to the pressure of the See also:

• ATMOSPHERE (Gr. fir µ6r, vapour; orkaipa, a sphere)

atmosphere minus 15 mm . Hg—while the vascular system of the rest of the body bears the full atmospheric pressure . The thin-walled auricles and veins yield more to this elastic traction than the thick-walled ventricles and arteries . Thus inspiration exerts a suction action, which furthers the filling of the veins and auricles . This action is assisted by the positive pressure exerted by the descending See also:

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

diaphragm on the contents of the See also:

• ABDOMEN (a Latin word, either from abdere, to hide, or from a form adipomen, from adeps, fat)

abdomen . Blood is thus both pushed and sucked into the heart in increased amount during inspiration .

Experiment has shown that the blood vessels of the lungs when distended are wider than those of collapsed lungs . Suppose an elastic bag having minute tubes in its walls be dilated by blowing into it, the lumina of the tubes will be lessened, and the same occurs in the lungs if they are artificially inflated with air; but if the bag be placed In a glass See also:

• BOTTLE (Fr. bouteille, from a diminutive of the Lat. butta, a flask; cf. Eng. " butt ")

bottle, and the pressure on its outer See also:

• SURFACE

surface be diminished by removing air from the space between the bag and the side of the bottle, the bag will distend and the lumina of the tubes be increased . Thus it is evident that inspiration, by increasing the calibre of the pulmonary vessels, draws blood into the lungs, and the movements of the lungs become an effective force in carrying on the pulmonary circulation . It has been estimated that there is about one-twelfth of the whole blood quantum in the lungs during inspiration, and one-fifteenth during expiration . The great degree of distensibility of the pulmonary vessels allows of frequent adjustments being made, so that within wide limits,as much blood in a given time will pass through the pulmonary as through the systemic system . The limits of their See also:

• ADJUSTMENT (from late Lat. ad juxtare, derived from juxta, near, but early confounded with a supposed derivation from justus, right)

adjustment may, however, be exceeded during violent muscular exertion . The compressive action of the skeletal muscles returns the blood to the venous cistern, and if more arrives than can be transmitted through the lungs in a given time, the right heart becomes engorged, breathlessness occurs, and. signs of venous congestion appear in the flushed See also:

• FACE (from Lat. fades, derived either from facere, to make, or from a root fa-, meaning " appear "; cf. Gr. cbatvstv)

face and turgid veins . The weaker the musculature of the heart the more likely is this to occur; hence the breathlessness on exertion which characterizes cardiac affections . The training of an See also:

• ATHLETE (Gr. aOX177'7r; Lat. athleta)

athlete consists largely in developing and adjusting his heart to meet this See also:

• STRAIN (through O. Fr. straindre, estraindre, mod. i treindre, from Lat. stringere, to draw tight, related to stress, stretch, string, &c.)

strain . Similarly the weak heart may be trained and improved by carefully adjusted exercise . Rhythmic See also:

• COMPRESSION

compression of the thorax is the proper method of resuscitation from suffocation, for this not only aerates the lungs, but produces a circulation of blood . By compressing the abdomen to fill the heart, and then compressing the thorax to empty it, the valves meanwhile directing the flow, a pressure of blood can be maintained in the aorta even when the heart has ceased to beat, and this if patiently continued may See also:

• LEAD
• LEAD (pronounced iced)

lead to renewal of the heart-beat .

There is no certain evidence that the pulmonary arteries are controlled by vaso-motor nerves . In the intact animalformed by the confluence of the mesenteric veins with the Portal splenic vein, which together drain these capillaries . The ctionrcala- portal blood breaks up into a second plexus of capillaries . within the substance of the liver . The hepatic veins carry the blood from this plexus into the inferior vena cava . Ligation of the portal vein causes intense congestion of the abdominal vessels, and so distensile are these that they can hold nearly all the blood in the body: thus the arterial pressure quickly falls, and the animal See also:

• DIES, CHRISTOPH ALBERT (1755-1822)

dies just as if it had been bled to See also:

• DEATH

death . The portal circulation is largely maintained by the action of the respiratory pump, the peristaltic movements of the See also:

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

intestine and the rhythmic contractions of the spleen; these agencies help to drive the blood through the second set of capillaries in the liver . The systole of the heart may tell back on the liver and cause it to swell, for there are no valves between it and the inferior vena cava . Obstruction in the right heart or pulmonary circulation at once tells back on the liver . The increased respiration which results from muscular exercise greatly furthers the hepatic circulation, while it increases the See also:

• CONSUMPTION (Lat. consumere)

consumption of food material . Thus exercise relieves the over-fed man . The liver is so vascular and extensile that it may hold one-See also:

• QUARTER (through Fr. from Lat. quartarius, fourth part)

quarter of the blood in the body . The circulation of the See also:

• BRAIN (A.S. braegen)

brain is somewhat peculiar, since this organ is enclosed in a rigid bony covering .

The limbs, glands and viscera can expand considerably when the blood pressure rises, but the expansion of the brain is confined . By the The expression of venous blood from the veins and sinuses the cerebra ! brain can receive a larger supply of arterial blood at c/rcu/a- each pulse . Increase in arterial pressure increases the tlon. velocity of flow through the brain, the whole cerebral vascular system behaving like a system of rigid tubes' when the limits of expansion have been reached . For as the pressure transmitted directly through the arteries to the capillary veins must always be greater than that transmitted through the elastic wall of the arteries to the brain tissue, the expansion of the arteries can-not obliterate the lumina of the veins . The pressure of the brain against, the See also:

• SKULL

skull wall is circulatory in origin: in the See also:

• INFANT (in early forms enfaunt, enfant, through the Fr. enfant, from Lat. infans, in, not, and fans, the present participle of fari, to speak)

infant's fontanelle the brain can be felt to pulse with each heart-beat and to expand with expiration . The expiratory impediment to the venous flow produces this expansion . A blood See also:

• CLOT, ANTOINE

clot on the brain or depressed piece of bone raise the brain pressure by obliterating the capillaries in the compressed area and raising the pressure therein to the arterial pressure . The arterial supply to the brain by the two carotid and two vertebral arteries is so abundant, and so assured by the See also:

• ANASTOMOSIS (a Greek word in which the second o is long, from avaaroµovv, to furnish with a mouth or outlet)

anastomosis of these vessels in the circle of See also:

• WILLIS, NATHANIEL PARKER (1806-1867)
• WILLIS, THOMAS (1621-1675)

Willis, that at least two of the arteries in the See also:

• MONKEY

monkey can be tied without See also:

• GRAVE

grave effect . Sudden compression of both carotids may render a man unconscious, but will not destroy See also:

• LIFE

life, for the centres of respiration, &c., are supplied by the vertebral arteries . The vertebral arteries in their passage to the brain are protected from compression by the cervical vertebrae . Whether the muscular coat of the cerebral arteries is supplied with vaso-motor nerves is uncertain .

Hurthle and others observed a rise of pressure in the peripheral end of the carotid artery on stimulating the cervical sympathetic See also:

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

nerve . The writer found this to be so only when the cervical sympathetic nerve was excited on the same side as the carotid pressure was recorded . If the circle of Willis was constricted, excitation of either nerve ought to have the effect; it is possible that the effect was produced by the vasoconstriction of the extra-See also:

• CRANIAL

cranial branches of the carotid . After establishing an artificial circulation of the brain Wiggins found that 'adding adrenalin to the nutritive fluid reduced the outflow, and it is supposed that adrenalin acts by stimulating the ends of the vasomotor nerves, rather than by stimulating the muscular coats of the arteries . The veins of the pia and dura mater have no See also:

• MIDDLE

middle muscular coat and no valves . The venous blood emerges from the skull in man mainly through the opening of the lateral sinuses into the See also:

• INTERNAL

internal jugular vein; there are communications between the cavernous sinuses and the ophthalmic veins of. the facial system, and with the venous plexuses 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 . The points of emergence of the veins are well protected from See also:

• CLOSURE (Fr. clooture)

closure by compression . The brain can regulate its own blood supply by means of the cardiac and vaso-motor centres . Deficient supply to these centres excites increased frequency of the heart and constriction of the arteries, especially those of the great splanchnic area . Cerebral excitement has the same effect, so that the active brain is assured of a greater blood supply (Bayliss and L . Hill) . In each unit of time the same quantity of blood must, on the average, flow through the lesser and greater circuit, for otherwise the The a circulation would not continue .

Likewise, the average The Non velocity at any part of the vascular system must be incul during versely proportional to the total cross-section at that part . muscular In other words, where the bed is wider, the stream is slower; actin #y. the total sectional area of the capillaries is roughly estimated to be 700 times greater than that of the aorta or venae cavae . Any general change in velocity at any section of this circuit tells both backwards and forwards on the velocity in all other sections, for the average velocity in the arteries, veins and capillaries, these vessels being taken respectively as a whole, depends always on the relative areas of their total cross-sections . The vascular system is especially constructed so that considerable changes of pressure may be brought about in the arterial section, without any (or scarcely any) alteration of the pressures in the venous or pulmonary sections of' the circulatory system: A' high-pressure See also:

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

main (the arteries) runs to all the organs, and this is supplied with taps; for by means of the vaso-motor nerves which 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 the diameter of the arterioles, the stream can be turned on here or there, and any part flushed with the blood, while the supply to the remaining parts is kept under control . Normally, the sum of the resistances which at any moment opposes the outflow through the capillaries is maintained at the same value, for the vascular system is so co-ordinated by the nervous system that dilatation of the arterioles in any one organ is compensated for by constriction in another . Thus the arterial pressure remains constant, except at times of great activity . The great splanchnic area of arterioles acts as " the resistance See also:

• BOX
• BOX (Gr. irl or, Lat. buxus, box-wood; cf. 2r6Eir, a pyx)

box " of the arterial system . By the constriction of these arterioles during mental or muscular activity the blood current is switched off the abdominal organs on to the brain and muscles, while by dilating during rest and digestion they produce the'contrary effect . The constriction of the splanchnic vessels does not sensibly diminish the capacity of the total vascular system, for the veins possess little See also:

• ELASTICITY

elasticity . Thus variations of arterial pressure, brought about by constriction or dilatation of the arterial system, produce little or no effect on the pressure in the great veins or pulmonary circuit . The contraction of the abdominal muscles, on the other hand, greatly influences the diastolic or filling pressure of the heart . It is obviously of the utmost importance that the heart should not be over-dilated by an increased filling pressure during the See also:

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

period of diastole .

When a man strains to lift a heavy weight he closes the glottis, and by contracting the muscles which are attached to the thorax raises the intrathoracic pressure . The rise of intrathoracic pressure See also:

• AIDS

aids the pericardium in supporting the heart, and prevents over-dilatation by resisting the increase in venous blood pressure . This increase results from the powerful and sustained contraction of the abdominal and other skeletal muscles . In the See also:

• DIAGRAM

diagram already given it is clear that the contraction of T will counteract the contraction of A . At the same time the rise of intrathoracic pressure supports the lungs, and prevents the blood, driven out from the veins, from congesting within the pulmonary vessels . Over-dilatation both of the heart and lungs being thus prevented, the blood expressed from the abdomen is driven through the lungs into the left ventricle, and so into the arteries . So long as the general and intense muscular spasms continue, there is increased resistance to the outflow of the blood through the capillaries both of the abdominal viscera and the limbs . The arterial pressure rises, therefore, and the flow of blood to the central nervous system is increased . The rise of the intrathoracic and See also:

• INTRA

intra-abdominal pressures, and the sustained contraction of the skeletal muscles, alike hinder the return of venous blood from the capillaries to the heart, and, owing to this, the face and limbs become congested until the veins stand out as knotted cords . It is obvious that at this See also:

• STAGE (Fr. 6/age; from Lat. stare, to stand)

stage the total capacity of the vascular system is greatly diminished, and the pressure in all parts of the system is raised . It is during such a muscular effort that a degenerated vessel in the brain is prone to rupture and occasion See also:

• APOPLEXY (Gr. arov n i.a, from aroaMvvew, to strike down, to stun)

apoplexy . The venous obstruction quickly leads to diminished diastolic filling of the heart, and to such a decreased velocity of blood flow that the effort is terminated by the lack of oxygen in the brain .

During any violent exercise, such as See also:

• RUNNING

running, the skeletal muscles alternately See also:

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

contract and expand, and the full See also:

• FLOOD (in O. Eng. flod, a word common to Teutonic languages, cf. Ger. Flut, Dutch vloed, from the same root as is seen in " flow," " float ")
• FLOOD, HENRY (1732-1791)

flood of the circulation flows through the locomotor organs . The stroke of the heart is then both more energetic and more frequent, and the blood circulates with in-creased velocity . Under these conditions the filling of the heart is maintained by the pumping action of the skeletal and respiratory muscles . The abdominal wall is tonically contracted, and the reserve of blood is driven from the splanchnic vessels to fill the dilated vessels of the locomotor organs . The thorax is tonically elevated and the thoracic cavity enlarged, so that the pulmonary vessels are dilated . At each respiration the pressure within the thoracic cavity becomes less than that of the atmosphere, and the blood is aspirated from the veins into the right side of the heart and lungs; conversely, at each expiration the thoracic pressure increases, and the blood is expressed from the lungs into the left side of the heart . While the respiratory pump at all times renders important aid to the circulation of the blood, its action becomes of supreme importance during such an exercise as running . The runner pants for breath, and this not only increases the intake of oxygen, butmaintains the diastolic filling of the heart . It is of the utmost importance that man should grasp the fact that the circulation of the blood depends not only on the heart, but on the vigour of the respiration and the activity of the skeletal muscles . Muscular exercise is for this reason a sine quit non for the See also:

• MAINTENANCE (Fr. maintenance, from maintenir, to maintain, support, Lat. manu tenere, to hold in the hand)

maintenance of vigorous mental and bodily health . Under the influence of the muscular system comes not only the blood but the lymph . The lymphatics form a subsidiary system of small valved vessels, and drain the tissues of the excess of lymph, which transudes from the capillaries of the organs during functional activity, or in con-sequence of venous obstruction .

The larger lymphatics open into the veins at the See also:

• ROOT (late O.E. rot, adopted from Scand., cf. Norw. and Swed. rot, Dan. rod; the true O.E. word was wyrt, plant, represented in Ger. Wurz or Wurzel; the ultimate root is the same in both words, and is seen in Lat. radix)
• ROOT, ELIHU (1845– )

root of the See also:

• NECK (O. Eng. hnecca; the word appears in many Teutonic languages; cf. Dutch ride, Ger. Nacken; in O. E. the common word was heals; cf. Ger. Hals)

neck . It is chiefly by the compressive action of the skeletal and visceral muscles, and the aspirating action of the respiratory pump, that the lymph is propelled onwards . It must be See also:

• BORNE, KARL LUDWIG (1786–1837)

borne in mind that the descent of the diaphragm during inspiration compresses the abdominal organs, and thus aids the aspirating action of the thorax in furthering the return to the heart both of venous blood and of lymph . The circulation remains efficient not only in the horizontal but also in the erect position, and just as much so when a man, l