LUNGS. 



animal, by wli!c]i tlie quantity and kind of air introduced 

 iiito the lungs can be regulated, and placing a fmalltube witli 

 a itopcock. in an artery, as the carotid or crural, which 

 enabled him to afcertain how the blood was altered. 



1. When the ftopcock is clofed iminediately after an in- 

 fpiration, the blood grows darker in thirty fcconds ; it has 

 acquired a deep tint in a minute, aild it poiTeflTes entirely the 

 appearance of venous blood in a minute and a half, or two 

 minutes. 



2. The produdion of the black colour takes place more 

 quickly by feveral fcconds, if the ftopcock be fhut after ex- 

 fplration, particularly if it has been a complete one. 



3. If tlie air be drawn out of the lungs by a fyringe, the 

 blood becomes immediately black : twenty or thirty fe- 

 conds are fuflicicnt for the change. No fuccelTive gradations 

 of colour arc obfervcd. 



4. If the lungs be extended by injefting air into thet'i, 

 and clofing the ftopcock, a longer time is necelTary for 

 changing the blood into the black Itate : three minutes will 

 then be required. 



Thefe phenomena are obferved in the pafTiige of the 

 animal from a Hate of afphyxia to death : a lerios of an 

 oppolite nature is feen when it is rellored from alphyxia to 

 life. 



1. When the ftopcock, after being clofed for fome mi- 

 nutes, is opened, the animal immediately performs fix or 

 foven great infpirations and exfpirations. A jet of red blood 

 fucceeds the black, which was flowing before ; and the in- 

 terval between the two is at moft thirty fcconds. There is 

 no fuccefllve change of tints, but a certain and decided alte- 

 ration. 



2. If a fmall quantity only of air be admitted, the change 

 of colour is lefs confiderable. 



3. If frcfh air be injefted, and the ftopcock then clofed, 

 the blood becomes red, but lefs manifellly than when 

 the air is admitted by voluntary refpiration : m the latter 

 cafe the animal firft expels the air that had become 

 fpoiled. 



4. If the air inclofed in the lung be drawn out by a fy- 

 ringe, and frefh air injefted, the change of colour is effefted 

 more rapidly than in tlie preceding caiie. 



J. When the lung is expofed by cutting through the 

 ribs, the circulation is continued for a certain time. If it 

 be alternately diitended and emptied by means of a fyringe, 

 the red and black colours are ItiU produced fo long as the 

 sirculation i.; kept up. 



From the rapidity i^ith which the blood, in thefe experi- 

 ments, is changed from black to red on opening the ftop- 

 cock, we caniujt help concluding tiiat the principle which 

 caufcs this alteration patTes diredly from the lung into the 

 blood, through the membranous lining of the air-cells. The 

 acceleration of the motions of the heart in animals undergoing 

 afphyxia, as in the famous experiment of Hook, by itijett- 

 ing air into the trachea, muft be referred to the red blood 

 penetrating the fibres of the heart, and putting an end to the 

 debility which the contaft of biack blood was producing. 

 Yet this method will never re-produce the motions of the 

 heart when they have been once annihilated by the contaft 

 of black blood. Bichat has often tr:ed this without fuc- 

 cefs. The heart, fays he, cannot be re-animated by the 

 aflion of the air, ur.lefs the blood, coloured by that fluid, 

 eould penetrate the organ. When the circulation is flopped, 

 how can this take place ? 



Hydrogen snd carbonic acid gafes were enip'oyed in re- 

 fpiration by filling bladders with them, and fixing them to 

 the tube in the trachea. The bldJder is a'ternaitly dirteiided 

 aAd emptied as tlie animal exfpires and infpires. He is at 



firft tolerably quiet, but in about three minutes begins to be 

 agitated ; refpiration becomes hurried and troubled, the 

 blood flowing from an artery grows darker, and is black at 

 the end of four or five minutes. Thtre was very little dif- 

 ference in the time required for the change, or intenfity of 

 the colour, whichever ot the two gafes was employed. 



The reafon why the change of colour takes place more 

 flowly when thefe bladders are adajited to the (tiipcock, than 

 when the latter is clofed, feems to be, that the air contained 

 in the trachea and its branches is repeatedly thrown from 

 the lung into the bladder, and vice -ver/a ; fo that its whole 

 refpirable proportion is fucceflively prefented to the blood. 

 This mqtion cannot take place in the latter cafe ; fo that as 

 foon as the pure part of the air contained in the bronchial 

 cells is cxhauftcd, the blood is no longer converted into tiie 

 red ftatc, although the trachea and its large divifions ftill 

 contain a confiderable quantity of air capable of ferving the 

 purpofes of refpiration. It appears that the converlion of 

 the blood goes on only at the extremities of the bronchial ra- 

 inincationi-, and that the internal furface of the large air- 

 veflels has no connection with this phenomenon. 



We have already feen that the action of the heart conti- 

 nues for fome time after the chemical phenomena of the 

 lungs have been interrupted ; the arterial circulation is there- 

 fore itill maintained, although the arteries contain a different 

 fluid from that which is natural to tliein ; and the organs of 

 the body, accuftomed only to the red blood, become pene- 

 trated, in confequence of this circulation, by black blood. 

 Bichat has proved this by cxpofing various parts in an animal, 

 while the itopcock in its trachea was clofed, and the animal 

 was confequently undergoing afphyxia. He has examined 

 in this way the mufcles, the nerves, the fkin, mucous and 

 ferous membranes, and the granulations of wounds, and 

 found that the black blood penetrated them all, and pro- 

 duced more or lefs confpicuous alterations in tfieir colour, 

 which was rendered either brown or livid. The phenomenon 

 is very obvious in the fliin, which always prefents more or 

 lefs extenfive livid fpots in afphyxia. Thefe can only be 

 explained by the exillence of an obilacle to the tranfmiffion 

 of the blood in the general capillary fyftem : in the fame 

 way we account for the fwelling of various parts, as the 

 cheeks, lips, and head in general. 



The black blood does not penetrate at all into fome parts 

 of the general capillary fyftem, and the natural colour is 

 confequently prcfcrved : in others it manifellly enters and is 

 obftrutted, producing a dark colour at the part, and more- 

 over a tumefaction, if it enters in large quantity : or, 

 laftlv, it may pafs this fyftem and enter the veins. In the 

 two former cafes the general circulatioB is arrcfted in the 

 capillary fyftem ; in the latter, which is the more ge- 

 neral, the courfe of the blood is fufpended in the capillaries 

 of the lungs. 



The faft that the black blood continues to be circulated 

 for fome time after the chemical phenomena of the lungs 

 have been interrupted, explains a phenomenon, which muft 

 have been obferved by all who are much employed in dif- 

 feftions ; viz. that in the dead body we meet with black 

 blood only, even in the veffels which naturally carry red 

 blood. However death may be produced, the functions of 

 the Inno-s are troubled in the lali moments of exillence, and 

 end before thofe of the heart. The blood ftill moves, al- 

 though it no longer receives the influence of the air : it is 

 therefore circulated black for a certain length of time, and 

 remains in that ilate in the organs, although tlie circulation 

 is much k'fb evident than in afphyxia. 



After having ftiewn that the interruption of the chen-.ical 

 phenomena of refpiration prevents the black blood from 



being 



