LUNGS. 



tieiJtion of Life witli Refpiration, Sec. ) An experiment, 

 winch any one may very eafily perform in his own perfon, 

 vill prove that point very calily. Lee him exfpire as fully 

 as polfible, and not inlplre again : the pnlfe is not changed, 

 and confeqiiently the circulation through the lungs is not 

 impeded. But the numerous and varied experiments of 

 Bichat place the fnbjeft beyond all doubt. Exhanft, fays 

 he, the lungs of an animal, by means of a fyringe mferted 

 in the trachea, and open the carotid artery. Here the cir- 

 culation ought to be fuddenly interrupted, according to the 

 common fuppofition, fmce the pulmonary veflels are reduced 

 from ihcir ordinary degree of diftention to tlie greateft pof- 

 fible collapfe and folomg : yet the blood continues for fome 

 ■time to be forcibly thrown out of the opened artery, and 

 muft confequently circulate through the lung in tliis (late of 

 extreme collapte. The fame circumftance is obferved when 

 the Inngs collapfe, in confeqtience of the thorax being 

 opened on both r!,des ; even if, ini\ddition to this collapfe, 

 ■%ve exhauft the air more effeftually with a 1) ringe. 



The pulmonary circulation is continued, and even per- 

 formed with facility, when collections of water, pus, or 

 blood, exill in ihe cheli, and diminifii, in a very confider- 

 able degree, the air-cells of the lungs ; and when, confe- 

 ■ quently, the angles and folds of the vcffels, if they are found 

 at all, muft be very confiderable. We may conclude, then, 

 that the interruption of the mechanical phenomena of refpira- 

 tion does not ilop the heart's aftion direftly ; but that it 

 operates indireftly, by cutting off the fupply of the ma- 

 terial, which is ncceflary for the exercife of the chemical 

 phenomena. 



The death which fucceeds to protrafted infpiration has 

 been afcribed to the mechanical diilention of the pulmonary 

 veflels by the air, which has been fuppofcd to impede the 

 circulation through them. But this explanation is as ill- 

 founded as that which we have jull confidcred. Diflend the 

 lungs of an animal by injecting a large quantity of air, and 

 ccnline this by a itopcock faftened in the trachea ; then 

 open the carotid artery. The blood continues to flow for 

 fome time with its natural freedom. 



Two opinions have been entertained concerning the man- 

 ner in which the interruption of the chemical phenomena of 

 the lungs produces a ceiTation of the heart's aclion. ■ Ac- 

 cording to Goodwyn, the black blood does not ftimulate 

 the left ventricle ,• fo that, in his manner ot viewing afphyxia, 

 death takes place, becaufe that cavity fends nothing to the 

 different organs. Its fource, therefore, is exclufively in the 

 heart. Biehat conceives, that when the chemical pheno- 

 mena of the' hmg£ are interrupted, there is a general aflec- 

 tion of all the organs : that the black blood carries to every 

 part debility and death, fo that the organs do not ceafe to 

 aft becaufe they receive no blood, but becaufe they receive 

 no red blood. The effefts of the contad of black blood 

 on the organs of the body wiU be illullrated prefently ; 

 we (hall confider here the phenomena of its contadt with the 

 parietes of the heart. 



Many circumilances (hew that the black blood is capable 

 of ftimulating the left ventricle, fo as to excite it to con- 

 traftion. If this were not the cafe, death fhould commence 

 in afphyxia with the ctflaticn of the heart's aftion, and the 

 annihilation of the fnnflions of the brain fliould be fecmdary. 

 But, kill an animal l:y ftopping the tra>.liea, by pbcing it 

 in vacuo, by drowni-: ; or inimerfion in noxious gales, &c. 

 and you will confta:;'ly obferve, that the animal hfe is lirlt 

 interrupted, that tl -. fenfations, motions, and voice are fuf- 

 pended, fo that the animal is dead externally, whi e the heart 

 ftill beats and the pulfe is kept up for fome time. The 

 different organs, therefore, do not ceafe to act in atpiiyxia, 



Vol. XXI. 



becaufe the heart fends them no blood, but becaufe it fends k 

 kind of blood which is not fuited to them. 



Let the trachea of an animal be flopped and an artery- 

 opened, the blood iffuing from the latter is at firft red, then 

 grows gradually darker, and at laft is black venous blood. 

 Neverthelef3,it is fliU expelled for fome time with confiderable 

 force. If the lungs be exhaufted by a fyringe, previous to 

 clofing the trachea, and an artery then opened, black blood 

 comes from it immediately, without going through the (hades 

 mentioned before, and a tolerably tlrong jet is kept up for 

 fome time. If the black blood did not poffefs the power of 

 exciting the left ventricle, its flow ihould be fuddenly inter, 

 rupted in this cafe, where it can undergo no change froav 

 th; Inng, and exifts in the aorta in the fame ftate as in the 

 venas cava:. 



It is moreover ftated by Biehat, that he lias rc-cxcited th* 

 contraftioiis of the left ventricle, after they had ceafed in 

 various kinds of violent death, by injefting black blood 

 through one of the pulmonary veins. It is obvious too, 

 that wiien lufpended refpiration is reflored by inflating the 

 lungs, the left ventricle mull firft propel the black blood with 

 which it is loaded, before the red blood can arrive at the 

 lungs. The heart of red blood has, therefore, the power 

 of impelling black blood into all the organs ; and in this 

 way we explain the peculiar colour of the different furfaces 

 in afphyxia. 



The mere contaft of black blood has no more fenfible 

 aftion on the internal furface of the arteries than on that of 

 the heart. If, when the trachea is clofed, an artery of the 

 foot be opened, the blood is propelled from it for fome time 

 with the natural force. 



" From thefe conliderations and experiments we may con- 

 clude," fays Biehat, " that the black blood has the power 

 of exciting the internal furface, and determining the aftion 

 «f the heart and arteries ; and that if no other caufe inter- 

 fered with their funftions the circulation might be continued, 

 not, perhaps, with equal force, but at leaft in a very fenfi- 

 ble manner. What then are the caufes which interrupt 

 the circulation in the heart of red blood and in the ar- 

 teries, 'when the lung tranfmits to them only black blood ? 

 For when the latter has flowed tor fome time, the jet is 

 gradually weakened, and at lall entirely ceafes : if the ftop- 

 cock fixed in the trachea be now opened, it is again fpeedily 

 reftored. I believe that the black blood afts upon the heart 

 as upon all other paj-ts, as we fliall fee that it influences the 

 brain, the voluntary mufcles, the membranes, &c. ; that is to 

 fay, by penetrating its tiffue, by debilitating each individual 

 fibre. 1 am well convinced, that if black blood could be 

 circulated in the coronary vcffels, while the red ihould pats 

 as ufnal through the left auric'e and ventricle, the circulation 

 would be interrupted almoft as quickly as in the preceding- 

 cafes." We conclude then, in general terms, and without 

 attempting to determine how this takes place, tliat the heart's 

 aftion ceaies when the chemical phenomena of the lungs are 

 interrupted, becaufe the black blood, which penetrates its 

 mufeular fibres, is not capable of keeping up their aftion. ■ 



In this view of the fubject, the right ventricle will be as 

 much affefled as the left, fince the black blood is diftributed 

 equally to the fibres of each. Yet the latter ceaies to aft 

 firft, and this is fo conllantly and well known afaft, that the 

 right fide of the heart has been called the- ii^timum moriens. 

 This arifes, as Haller has already clearly explained, from 

 the circumftance of the right cavities being- longer excited 

 than the left. (See Hear-i', and Circulation'.) It dot* 

 not prove that the left ventricle dies firfl in afpliyxia. If 

 that were the cafe, the left aiu-icle anc ventricle Ihould be 

 diftended with blood after death, and tliis diftention fliouM 

 4 M be 



