LUNGS. 



be propagated from them into tlie pulmonary veins and 

 right fule of the heart ; that is to fay, the cufgeftion of 

 blood ftiould begin in the refer^oir which firft ceafes to 

 aft, and it fhould be propagated from that into the others. 

 The examination of animals, who have perifhed from af- 

 phyxia, fliews us, on the contrary, that the cavities of red 

 blood and the pulmonary veins contain but a fmall quantity 

 of bhck blood in comparifon with that wliich diftends tliofe 

 of the oppofite fide ; that the point at whieh the blood has 

 ftoj'ped is principally in the lung, fiom which we are to 

 trace its ft jgnation in the whole venous fyftem ; and that 

 the arteries contain as much in proportion as the correfpond- 

 ing ventricle, fo that deathcannot be fuppofed to have begun 

 in it rather than in any other part. 



Bichat Hates afterwards, that he cannot entirely rejeft 

 <he notion of the lefs aptitude of the black blood to ftimu- 

 late the left ventricle. When an artery- is opened, a ftop- 

 cock being fixed in the tracl»ea and clofed, the iet of blood 

 is gradually weakened ; open the ftopcock, and the blood 

 becomes again immediately red, and is thrown out more 

 forcibly. This change is too fiidden to admit of our ac- 

 counting for it by the red blood penetrating the tilTue of 

 the heart. Yet it may happen from the powerful motions 

 of infpiration and exfpiration which the animal makes as foon 

 as air enters the chefl. For if an artery be opened, and 

 refpiration thus hurried, the jet of blood will he raanifeftly 

 increafed. On tlie whole, therefore, even if it be allowed 

 that red blood is a more powerful ftimulus to the heart than 

 black, the excefs mull be very trifling. 



In connexion with this fubjeft, we may confider the 

 explanation of the remarkably diftended ftatc, in which the 

 pulmonary artery, the right cavities of the heart, and the 

 venou? fyitem are found in in (lances where death commences 

 in the chemical phenomena of the lungs, compared with 

 the comparatively empty condition of the fyftem of red 

 blood. Tlie phenomenon is fo remarkable as to have attrafted 

 the attention of all who have opened the bodies of animals 

 killed by afphyxia ; it has been commonly explained by the 

 folds of the pulmonary vcfltls, which we have already con- 

 fidered. 



The lungs are found in tuo very different ftates, accord- 

 ing to the manner in which life ends : when death is inftan- 

 ■taneous, they are not loaded with b!ood ; the auricle and 

 ventricle of black blood, the pulmonary artery, and the 

 general venous fyllem, are not remarkably difiended. On 

 the contrary, when the chemical phenomena of refpiration 

 are flowly dellroyed, when an animal has been kept as long 

 as poflible in the diftrcfs and anguifti which attend inter- 

 ruption of the funftions of the lungs, thcfe organs are 

 extremely Uiaded with blood, and diftended to a volume very 

 far exceeding that which they prefent in the other cafe. In 

 whatever condition the lungs of an animal, which has pe- 

 rilhed by afphyxia, may be found, whether they be loaded 

 or empty, and conCcquently whether death have been brought 

 un flowly or fuddenly, the vafcular fyftem of black blood 

 is always full of this fluid, particularly about the heart ; 

 there is conftantly a great difference in this refpeft between 

 it and the vafcular fyftem of red blosd, and confequently 

 the principal obftacle to the circulation is in the lung. 



Bichat explains this phenomenon from certain ccnfider- 

 ations connected with the blood, the lung, and the heart. 



1. The black blood circukting in the arteries is inca- 

 pable of furnifhing to the organs of fecretion, exhalation, 

 and nutrition, the various materials neceflary for the exercife 

 cf thofe funftions ; or if it conveys the materials, it cannot 

 excite the organs. Hence, the venous fyllem receives an 

 tinufually large quantity of blood, as all Uiat portion, which 



is ordinarily removed by the funftions jufl mentioned, enter* 

 it ; and the difficulty of tlie pafTage through the lungs i» 

 proportionally augmented. All obfervers have been ftruck 

 by the gnat abundance of blood found in the veftels in 

 thefe cafes. 



2. The lung is no longer excited by red blood : the^ 

 bronchial vclTels carry black blood to it, and hence its 

 powers are enfeebled, as thofe of the heart are by the fame 

 fluid conveyed to it by the coronary arteries Again, the 

 pulmonary capillary iyftem contains nothing but black 

 blood. I'hat the tonic powers, by which the circulation is 

 carried on in thofe velTels, muft be much depreffed from 

 this caufe, cannot be doubted. Moreover, the habitual 

 excitation of the mucous furfaces by the atmofphei-ic air 

 is interrupted ; and this muft aflttft in lowering the tonic 

 powers. 



3. Tlie auricle and ventricle of black blood aft more 

 weakly, and are Itfs capable of furmounting any refiftance 

 in the lung in confequence of their fibres being penetrated 

 by black blood. They can no longer refill the blood 

 brought by the \en.T cavx, and become diftended bj it. 



Thefe confiderations feemto account fatisfaflorily for the 

 diftention of the fyftem of black blood in afphyxia ; ws 

 have next to explain why the fyftem of red blood contains a 

 quantity comparatively fo fmall. As the obftacle exifts in 

 the lungs, a fmaUer quantity arrives at the left fide of th« 

 heart. The natural ftrength of the left ventricle and the 

 arteries exceeds that of the right and- the veins ; confe- 

 quently the former can more ealily overcome the rcfiftanca 

 of the capillaries of the body in general, than the latter 

 can that of the pulmonary capillaries. Again, there is 

 only one caufe of retardation in the general capillary circu- 

 la'ion, •viz. the contaft of black blood with the organs j 

 while there is added to this caufe in the lungs, the ablcnce 

 of the habitual excitation produced by the atmofpheric air. 

 Thus, we find in the lungs more refiftance to the blood 

 brought by the veins, and lefs force to overcome that re- 

 fiftance ; while in the body in general the obftacles at the 

 jimftion of the arteries and veins are more feeble, and the 

 force tending to overcome them is greater. 



Although the general capillary fyllem offers lefs refiftance 

 to the arteries, than the pulmonary capillaries do to the 

 veins in afphyxia, yet there is a manifeit obftruftion evea 

 here ; and it gives rife to two remarkable phenomena. 

 Black blood is coUefted in the arteries in a much greater 

 quantity than ufual, although in a fmaller proportion than 

 in the veins ; hence injeftion fucceeds badly in fuch fubjefts. 

 The accumulation of black blood in the extremities of the 

 arteries gives a livid colour to all the furfaces of the body, 

 and a bloated apjiearance to the various parts, as the face, 

 tongue, lips, &c. Thefe two phenomena indicate a con- 

 geftion ol black blood in the arterial extremities, as the ana- 

 logous appearances of the lungs denote a difScuIty of paf- 

 fage through the pulmonary capillaries, where indeed thje 

 congeftion is much more manifeft, becaufe the fyftem is con- 

 centrated within a fmall fpace, while the other is fpread 

 over the whok- body. 



Influence ivhich the Dtath of the Lung produces on that of the 

 Eratu. — The black blood afts upon tiie brain as it does on 

 the heart ; that is, by penetrating its tiffae, and depriving 

 it of the excitation neceffary for keeping up its aftion. 

 What we have faid concerning the heart is therefore equally 

 applicable to tliis fubjeft. The experiments of Bichat on 

 this point have been very numerous and diverfified. He 

 firft transfufed through a tube the blood of the carotid of 

 one dog into the carotid of another : this does not hurt the 

 animal if a vein be opened to obviate plenitude of the veffels. 



