. 



HDAKT. 



laatofafroc (from vhioh th* aanaxad highly 

 to taken), or In the trantparvot rwru of other 

 i** BM. UiH or lung* of B*h. frog*, lixard*, Ac., we *ee 



in little (tram*, in 

 multitude, M in the venels which kit 



oAcMUr Large to admit several to p.- together, t other, in unly 

 afcagle iiw, where the nml U bat little larger tana the globule 

 taect Here and then a (lobule U Ma to be checked in it* conne. 



M if the cane] were too narrow for iU piage ; then it turn* a little, 

 ad e>kia roll* on. The current* run generally in the eame dinctiou 

 i*> the eune Mtoili. all Uoding to larger branch, which may be 

 reyuiliil M Ike eimiuienneejieiit of rrin, UK! setting out from the 

 uaotoet tsrouaetioa of the artry. The capillaries are the moet 

 deiioate of all organic Umum, measuring from 1 -2000th to 1 fiOOOth 

 >( an inch hi iltoiaiiir ; they exist in all tutuee of the body, varying 

 id 11 1 IIM*JI ! only in th greater or leas oloeeaee* of the network 

 which thry form, and of which the meehe* are in aome organi *o 

 fake a* no* to cured U width the Hiamrttr of the oapillarie* them- 

 alra. a. i* t he oas. in the iris and lung*. It i* through theee veeaal* 

 thai aU UM important prueisa** of accretion, nutrition, and ab*or|.ti..n 

 re iftnlil. tor there u DO mfflci*nt evidence for believing in the 

 xiatoee of a till more minute errie* traTcned only by the colourleu 

 parte of the blood, and which MUM bare deacribed a* vas* aeroea, 

 nm rxkaUnUa, Ac. Bat hitherto no preeiM observation* have been 

 aade oo the manner in which theee proem** are performad ; no 

 pone CM be diaeovemd at the aide* of the capillarie* for the pateage 

 of aide, which it i* therefore probable i* effected by aimple tmnsmU- 

 ix ; o--r can any open termination* be Men, for all appear to ariao 

 froa* arteriea and Urmicale in 



Th* tojtnenn* of th* minutest arterie* and vein*, and of the capil- 

 larie*, on the circulation, ia beat ae*o in the phenomema of local 

 aclton. aa inflammation, bliuhing. turgvscence. ftc. If the web of a 

 fM*/a foot pUe*d in a microscope be irritated, the capillaries are *een 

 , *o a* aometim** to prevent the flow of blood 

 if the itimuln* be so gnat a* to produce inflam- 

 th*n thry dilate, and a larger number of globule* 1* seen 

 BMBBf along them with gnat rapidity. The same may be seen in the 

 IMUMB rye. the vnuli in th* front of which are so minute that they 

 give a colour to it : bat if they be irritated by a particle of dust, at 

 **e* Ukrjr dilate, and more blooiglobule* entering them, they are *een 

 a* tortuous canal* 6IUI with Mood. On a larger scale one see*, after 

 woond or oth*r injury, the part* around grow redder, and swell 

 tnm the aslui of hlood to it* capillarie* ; and if the inflammation 

 * in a part which can be compared with another similsr one, a* in 

 the hand. <*M (*! that the pulse U fuller and stronger on the injured 

 than on th. *oond aid*, indicating that a larger quantity of blood i* 

 i U, A Ml tor* evident accumulation of blood i* 

 , in which, from a mental impression, in an instant 

 ' i of the nee, neck. bead. *c., become distended 

 . Mat of fear is produced by the opposite Condi- 

 Waal, add we hate other caw in which a decrease of the quantity of 

 Mood in a part U Man In th. deficient nutrition and shrinking of part* 

 which have beam* niilmi, aa in the nib of tadpoles, the bom* of 

 aW. ft*. All the oina*ane are cUarly .ufflcient to prove that. 



I clearly sufficient to prove that, 



of any miiwno. extending from the heart or arteriea, 

 iWr. m th. T.ry minute Tea, 1. of til parte a power by which the 

 of hlood nito.ua; through them may be either iucreaaed or 

 jfced. whether it be oWted by an alteration in the propelling 

 r of th* vinili thnlvea. or. a* *ome imogin-. by an increased 



i and the blood. An expla- 



i of the at*. **.* which attend this circulation, independent of 

 the heart, ha* ban o*red by ProfMor Draper of New YorV:- 



ll to ,W. of braw ihown. by pmmenU on inorganic bo,lie*. 

 U- ,f t.. linukU nn.jMiuiiiu.li with wh other through a capillary 

 walk of which they have both an affinity, but this 

 Uquid than in th* oth*r, a movement will 



lly to*, th. toha. anddrivim the other before it. The *un. 

 n when the fluid U drawn, not into a (ingle tube but into 

 .***'"'* tab " Prmealing a .li.l Urncture j for if thi* porou* truo- 

 t*ab*.*vjowytratea with th. fluid for which it ha* the lee* degree 



of attraction, thi* will be driven out and replaced by that for u hk h 

 it ha* the greater affinity, when it i* permitted to ttlmorb tliU. 

 if iu it* paaaage through the porou* aolid the liquid uudurgo such a 

 change that it* affinity be diiuinube.1, it U obvious that, ocomliug to 

 the priuciple jiut explained, it inunt be driven out by a fresh aupply 

 of the origiuml liquid, and that thus a continual movement in thu 

 am* direction would be produced. Nw tbin i< piecuely what 

 eem* to take pUce in an organised tissue which Is permeated by a 

 fluid, between whoea particle* and those of the tissue which it 

 tratee, affinitie* exist which are concerned iu the formative change* 

 that have already occurred, and thu* iu the circulation of the nutri- 

 tive fluid there is a constant attraction of it* particle* towards the 

 wall* of the veaael*, ud a continual aeries of changes produced iu the 

 fluid a* the result of that attraction. The fluid which has given up 

 to a certain tissue some of it* materials, no louger has the same 

 attraction for that tissue; and it is consequently driven from it by 

 the superior attraction then poeaened by the tissue for another por- 

 tion of the fluid which i* ready to undergo the same change*, to be 

 in it* turn rejected for a fresh supply. Thus, in a growing part 

 there must be a constantly renewed attraction for that portion of the 

 nutritive fluid which ha* not yet traversed it; whilst, on UK 

 baud, there is a diminished attraction for that which has yielded up 

 the nutritive materials required by the particular tiiuea of the part; 

 and thus the former is continually driving the latter before it. lint 

 the fluid which is thus repelled from one part may still be attracted 

 toward* another, because that portion of its contents which the lutU-r 

 require* may not yet have been removed from it, and in this manner 

 the current may be maintained through the whole capillary network 

 until the liquid has been entirely taken up by the tissue* which it 

 permeate*." 



" The source of the movement being thus attributable to the 

 formative action* to which it is subservient, it is obvious that it must 

 be effected by any external agencies which quicken or retard these ; 

 and it is thus that the influence of heat, cold, and electricity upon the 

 rate of the flow seem* most readily explicable." ((.'ui-pciitrr, ' Princi- 

 ples of Physiology.') 



It will be seen that these elementary facts may be employed 

 to explain the nature of the capillary circulation, and here again we 

 may quote Dr. Carpenter's explanation of the phenomena: 



"It will be convenient to take the respiratory system as an example 

 of it* application ; since the changes to which this is subservient are 

 more simple than those which take place els where. The venous 

 blood transmitted to the lungs, and the oxygen in the pulmonary urlU 

 have a mutual attraction, which is satisfied by the exchange of " 

 and carbonic acid that takes place through the wails of the cupil- 

 larie* ; but when the blood has become arterialised, it no longer bos 

 any such attraction for the air. The venous blood therefore will 

 drive the arterial blood before it in the pulmonary capillaries, whilst 

 respiration is properly going on ; but if the supply of oxygen be inter- 

 rupted, so that the blood is no longer aerated, no change in the 

 athnitie* take* place while it traverses the capillary network ; the blood 

 continuing venous still retain* it* need of a change, and its attraction 

 for the wall* of the capillarie* and iU egrets into the pulir.na: y Min- 

 is thus rousted rather than aided by the force generated in the lungs. 

 In the systemic circulation the changes are of a much more complex 

 nature, every diitinct organ attracting to itself the peculiar substance* 

 which it require* a* the material* of its own nutrition ; and the 

 nature of the affinities thus generated will be consequently mil. ivnt 

 in each case. But the same law holds good iu all instances. Time, 

 the blood conveyed to the liver by the portal veiu contain* the mate- 

 rial* at the expense of which the bile-secreting cells ore develop, d : 

 consequently, the tissue of the liver which is principally made up ut' 

 these cells possesses a certain degree of affinity or attraction for blood 

 containing theee materials, and this is diminished so soon as they 

 have been drawn from it into the cells around. Conseijii. ntly, tliu 

 blood of the portal vein will drive before it into the hepatir vein thu 

 blood which has already traversed the capillaries of the portal s\ 

 ami which has given up, in doing *o, the elements of bilo to the solid 

 tissue* of the liver. We are now pn-jjared, therefore, to understand 

 the general principle that the rapidity of the local circulation of a part 

 will depend in great measure upon the activity of the functional 

 change* taking place in that part the heart's action, and the state of 

 the general circulation remaining the same. When, by tin 

 vitality, or the unusual exercise of any organ, the changes which th.i 

 blood naturally undergoes in it are increased in amount, the affinities 

 which draw the arterial blood into the capillaries are stronger, and 

 are more speedily satisfied, and the venous blood is therefore <l 

 out with increased energy. Thus, a larger quantity of blood will 

 pan through the capillaries of the part in a given time without any 

 enlargement of their calibre, and even though it be somewhat dimi- 

 nished ; but the sice of the arteries by which it is conveyed soon 

 undergoes an increase in the supply of blood, alogethcr irrex|>ectivo 

 of any change iu the heart's action. This principle has long hc.-u 

 known, and baa been expressed in the concise adage, ' Ubi stimulus 

 ibi fluxus,' which those physiologists who maintain that the circula- 

 tion is maintained and governed by the heart alone, cost into unmerited 



: -. .. 



Following the course of the circulation, we come now to the veins, 



