v ..; 

 sad U*efci*f | 



i tAksaptae*. 



of UM heart oMrtnet Uwy are 

 heart 



of UM circulation 



r. The heart lying loosely in it* 

 UM mat vw**st pa** out of that 



(jtcantHna, a*4 tied oaOy wh*r UM (Treat v**a**l pas* o 

 w-a. fiwo UM blood which UM rentrioUa force 

 la* s> uK*d up. and atrika* at Mb wotriralar contraction, or 

 syatala.** M It eaUad, aa*t UM wall of UM eh**, producing that 

 (a.t.i whtth may be fU by the ffafar or hand plaeed just beneath 

 MM left bnart. and which ahvoai *atly ooiwU*at with the pulse 



out ; it* 

 contraction, or 



MtetUMwrM. At UM relaiatina. or diaatoU. of 

 *r *) sMiwatopa, * or a*w UM part whar* UM I 



ata. ooliBlilsMly with which 

 wall .* UM ch**. 



> diartolc. of tb* ventricle* they 



IUL Tb*l*M iVjtiotW 



be placed directly, 



. whar* th* heart i* felt beating, 

 i* beard coincidently with the 

 ____rfy followed by* second *ound, 

 deflMd, like the falling; back of a light 

 UM heart Mama to fall back from th* 



<. 



UM Br kBf amind u **niin heard. They Uke place in regular rhyth 



ach two impulse* of t 

 occupy two, the awood 



r Bf amin u **nin ea. 



Iitia UM whole period ooeanfad brtwmi each two impulse* of the 

 (ft into four part*, MM flnt *ound would occu 



It w nicwesaatry to mllu.U to various explanation* given of those 

 mad*. ll*y w<*r* B<M th* subject of *n exteneiv* *erie* of expert- 

 Mrti by oMBfaittM of UM Brituh Aawciation, which were reported 

 at UM nrhi>i in IMP and 1887. From the** and other experiment* 

 may 

 of UM n 



i in IMP and 1887. From the** and other ex 



that UM Ant aoond i* prodaoed by the vibrations 

 6bn at UM ventricle* daring their contraction, and 



by U* nh of UM blood through the na 

 aorta and pulmonary artery, *aitnl in 



p 



leading to the 



a very slight degree by the 



vibiaUmi of UM heart atnking against th* chat. The second sound 

 fa all probability UM result of UM falling back ami consequent 

 i of UM asmllnnar valve* when the blood just expelled from the 

 iwitatoa. The succession of action* in the heart has 

 UM eantnetion of the auricles is coincident with the 

 paiMP, for their vermicular and alight contraction doe* not produce 

 aay audible vibration*; the pans* hut* till the ventricle* are com- 

 pletely dMhUKMd by th* contraction of the auricle* : then come* the 

 lot M*d ouincidroUy with the ventricular contraction, the forcing 

 af UM blood into UM arterial, UM elevation of the valves to prevent 

 UM blood Iron going into the auricles, and to permit it to go into the 

 art*ri. UM impuUe of the heart against the wall of the chert, the 

 pulsation of UM irreat arteries, and followed after a scarcely appreciable 

 patiod by UM pal** at the wrirt and other part* distant from the heart. 



Lastly, the 



sound i* heard ooincidently with the relaxation of 



UM tirtitol**, UM falling down of the valve* to permit the t.WI t,, 

 aw Awn UM aoriela* into UM ventricle*, and to prevent it* pawing 

 fraa* the arteriea back into UM ventricle* ; and the rush of blood from 

 UM aortal** into UM ventricle*, which continue* through the whole 

 tssMof UM Quit aound *>d the pause. 



At raeh uuBtiautlim of UM ventricle* a very Urge proportion of tho 

 bfcod which they contained U expelled into the artoriea, and a very 

 ItttU May tow hack into UM auricle*, e*pecially the riirht. before the 



be ex 

 Mood 



producing the slight dilatation of the 

 ly often be seen at each contraction of the 

 At eaeh contraction of the auricles also it i* probable 

 blood tow* back into the cavaj and pulmonary veins, for 

 are * distended rather more suddenly at this time than can 

 Iptatoed by UM men street and consequent accumulation of 

 I fa UMSD. However, so large a portion of the heart'* power is 



ver, *o large 



fa propelling UM Mood into the arterie* that them (light 

 " la UM eoatrary diractioa need acaroely be taken int.. 

 ta aihmlMhal iu atnonnt At each oontraction of the 

 about aa ouaoe and a half of blood i* foroed into each 

 artery, with MM* force, that Halw found that the blood a* it nubed 

 frMa UM opi vaaia artrry in the thigh of a hone would riaa 8 or 8 

 (ret t*j a gbM. tab* of the am* (in aa th* vre], while in the 

 !! i id artery of a (hem U roe* 64 fort, and in tho* of don from 

 4J. MM. KiiMdll. (Mageodie-* -Journal d* Pbyalologi?) al*. 

 aalHOBM, by diiliiMioM from accurate experiment* on animal*, that 

 UM fare* of the blood *. Hrtream* la the human aorta w*. .uffi- 

 laM to nafott a wibt of 4 Ib*. Sdr. 48gra. Now, if the quantity 



iSTi tot !".? >lo *'Vy U ~~ m 1 * W P ""^ (troy weight), 

 wfcVh to proUMjr abort an accurate averag*. and if an ounce and a 

 half b. farced fro UM vmtricle at each twbmUon, of which, on an 

 r* 70 per minut*. a portion of blood will go th* 

 of UM ci 



lation to boot 3( minute*, which U 

 rate than w* night d*duc* from th* 

 >( Maria* (TWdemann'. 'ZaitaohrifV t J), who found 

 iajMted fatto the vein* of bone* omild be detected in 

 in half a minute, 



the heart to be the eol* agtnt by which th* 

 , but it i* orrtaia that **rral other agent* 

 That tb* heart ha* bowerer an InOueno* 

 -a*M|,.rU^UMem.W.ion UquiUwident. In th* larger arteri*. 

 *.+!+* mm fanh.laer.aat of UM curm.1 which lAad K t in 

 *+, u M coMdw. with b. *ortetto.ofUMcU.; 





lll'.AUT. 40 



in the cmaller once, by the mine increa** at a oaroely appreciable 

 interval ; in the capillariea, by the occasional pubatile motion which 

 may be Men in them, when, after an animal ha* been largely bled, ita 

 traniparent part* are examined with the microscope, and thin though 

 the heart U acting very weakly. Lnrtly, in the veins we nu.l it* 

 influence still exerted; for if the main nrtcry and vein in n limb be 

 expoaed and isolated, anil tho latter be wounded, the flow of blood 

 from the orifice may be exactly regulated by oumprauing the artery, 

 that i*, by preventing, to a greater or leu extent, the blood from 

 flowing to the vein with tho impulse given to it by the heart There 

 are cue* again in which the veins have distinctly pulsated, and the 

 pulsations nave been clearly proved to have been communicated from 

 the heart through the capillaries. To these we may add that the 

 rapidity of the current in the arteries, reins, and capillaries, is always 

 in direct proportion to the strength and frequency of the ventricular 

 contraction, and always more rapid in the porU near them than in 

 those remote from the heart ; that it cease* in all the instant the 

 heart -is removed, or it* influence on a part cut off l>y <livi<ling the 

 main artery ; that in old persona, iu whom the whole arterial system 

 of the lower extremities is sometimes ossified and rendered incapable 

 of contraction, the heart alone is sufficient to maintain the circulation 

 through the affected parts ; while, on the contrary, when tho heart's 

 power is by any cause weakened or interfered with, partial stagnation 

 and an extremely languid motion of the blood is found in all the 

 organ*. In cases of suspended animation no motion of blood 

 can be produced till the heart begins to act ; but when this is the 

 case, it has of itself sufficient power to set all the blood of the body 

 in aVurrriit. 



'I'hi-e are so many proofs that the contraction of the ventricles ha* 

 a (hare in propelling the blood throughout the whole course of the 

 circulation ; but the heart also assists, by the enlargement of itx cavi- 

 ties after their contraction, which, whether it be the effect of mi ro 

 elasticity, or of an active power of dilatation, certainly takes place 

 with great force. The heart, in short, acts at once as a forcing ami as 

 a sucking-pump. The proofs of this are, that the auricles, and still 



tho ventricles, dilute, 



4 not gradually, but suddenly, 



and with more force than 

 they could be distended by 

 the blood being impelled 

 into them ; that the currents 

 observed in living aiiinmU 

 are often seen to be increased 

 . ..in. i.l.'iitly with the dilata- 

 tion of the auricles ; by the 

 velocity of the flow of hl..,,,l 

 from the auricles into the 

 ventricles being dispr. 

 tionato to the degree of con- 

 traction of the former. 



From the heart the blood 

 is poured into the arteries, 

 a series of ramifying tubes 

 through which the current is 

 distributed, divided into a 

 gradually increasing nuniKei- 

 if streams, which progn-n- 

 nivelydiniinii<h in six.e, till it 

 arrives at a network of the 

 minute canals, tin' 

 capillaries. As a general 

 rule, when an arterial trunk 

 divides, tho sum of the 

 diameters of the branches is 

 greater than the diameter ol 

 the trunk tlniH in the an- 

 nexed diagram (in which 

 the arrows indicate tli" 

 course of the blood), tho 

 mini of the diameters of tho 

 branches 2, 2, is greateY than 

 that of 1, and the sum of 

 these of 3, 8, 3, greater than 

 that of 2, fr..in which they 

 arise. Hence the arterial 

 system has been compared in 

 t'cii-in tn a cone, nl' which the 

 heart is at the apex and 

 the stream of blood will 

 be. like a current gradually 



growing wider, so that if no additional impulse be given to it, it will 

 become slower as it become* more distant from the heart, an effect to 

 which the friction of the blood against the walls of the vessels will 

 *Jo contribute. The effect of both these causes however is so slight 

 that M. MaanJO* ho* found that the force of the current of blood in 

 all arteries sufficiently largo to be experimented on is relatively the 

 am* ; that in the aorta, for example, bears the same relation to its 

 diameter a* that in the artery at the wrist docs to its diameter. Thus 



1, trunk of the arl.ty; ?, 

 In!" which II >iilllvii| ( . ; 3, .mall branchm, 

 \f brrnmlng umallcr and rmallcr 

 until thrjr terminate In 4, the capillary 

 bianrhri. 



