RESPIRATION. 



! the living powers are about to ceafe. To us there 

 appears but one way of elcaping from thefe manifold diffi- 

 culties, vhich is limply to conclude, that the infpired air, 

 which is not returned, is retained in the cells of the lungs, 

 truch a fuppofition dillipates at once all anatomical and che- 

 mical difficulties, and explains why no air difappears in na- 

 tural refpiration, when the expiratory powers are in full 

 vigour and able to expel it, and why its difappearance in- 

 creafes in proportion as the actions of thefe powers decline 

 and ceafe. 



It is, however, worthy of remark, that, in thefe lafl ex- 

 periments, not only was there a diminution in the whole 

 bulk of air, but its relative proportions likewife varied ; 

 for, in IOO parts, the oxygen and carbonic acid amounted 

 together only to about two-thirds of the ufual quantity of 

 oxygen, and the deficiency was fupplied by a fuperabund- 

 ance of nitrogen gas. We are not prepared to fay why, in 

 this very embarrafled Mate of the refpiratory function, the 

 relative proportions of the expired air fhould thus vary ; 

 but the fact proves only the retention of oxygen in the 

 lungs, but not its abforption by the blood. Should it even 

 be maintained that oxygen was ablorbed, becaufe, in thefe 

 two experiments, a portion of it difappeared, then, by the 

 fame mode of reafoning, we mull alio contend, that, in the 

 thirteen preceding experiments, no abforption of oxygen 

 took place, becaufe no part of it was retained ; and as thefe 

 lall experiments alone come near to the natural exercife of 

 this function, they authorife us to conclude, that fuch fup- 

 pofed abforption of oxygen conltitutes no neceflary part of 

 healthy refpiration. In truth, in fome inllances where a 

 mixture of oxygen and hydrogen gafes was refpired, the 

 oxygen and carbonic acid in the expired air uniformly ex- 

 ceeded, by one per cent, the total oxygen infpired (Phil. 

 Tranf. 1809, p. 425-) ; from which it may be inferred, that 

 thefe variations in the proportions of the expired air pro- 

 ceed entirely from accidental caufes, and are totally inde- 

 pendent of any abforbent function in the lungs. Further 

 Inquiry, v. 2. ch. 4. 



If we are correct in reprefenting that the air undergoes 

 no diminution of volume in breathing, it will follow necef- 

 farily that no part of it can be abforbed in the lungs. This 

 notion of abforption is not only at variance with the refults 

 of the molt accurate direct experiments, but it is alfo re- 

 pugnant to our knowledge of the flructure of the lungs. 

 The finenefs of the ablorbing veflels, the mucus perpetually 



:ing the furface of the cells, the elaltic nature of air 

 ltfelf, fo that it neither penetrates moilt paper, cloth, nor 

 (kin — all demonllrale that no air gets into the blood by this 

 route. If, indeed, air were taken up by the abforbents, it 

 mult pafs to the right fide of the heart, and change the 

 colour of the blood there, which does not happen.] 



But if, either by the function of abforption, or by the 

 operation of chemical affinity, air did enter into the blood, 



.ay furely with rcafon demand fome proof of its pre- 

 fence ; yet, fays Haller, " Nulla unqu.nn in vivo calido ani- 

 rnali bulla acris in fanguine vifa ell." (Prims Lin. f. 306.) 

 This opinion is confirmed by the direct experiments of Dr. 

 Darwin ; for having inclofed a portion of the jugular vein 

 of a (heep between two ligatures, it was cut out, itripped 

 of its adhering cellular membrane, and then thrown into a 

 glafs of water of temperature ioo°, (landing under the rc- 



■r of an air-pump. It at once funk to the bottom, and 

 did not rile when the air was exhaulled ; nor, when after- 

 wards taken out, wiped dry, and laid on the floor of the 

 receiver, did it exhibit any fwelling under the exhaullion of 

 the veffel. The experiment was repeated with a limilar re- 



fult on a portion of the vena cava of a pig. Phil. Tranf. 

 v. lx';.. p. 545. 



Neither do the effects refulting from the admixture of 

 aeriform fluids with che blood, favour the notion of the en- 

 trance of air info that fluid. "Animal, cui acr in faneui- 

 nem inflatur," lays Haller, " nerit certo et velociter ; neque 

 quidquam fat is certi elt in fanguinis venarum pulmonaliam 

 aucto rubore." (Loc. cit.) This affertion is confirmed 

 likewife by direct experiment. When Dr. Girtanner in- 

 jected oxygen gas into the jugular vein of a dog, he cried 

 dreadfully, breathed quick, and died in three minutes ; 

 when nitrogen g thrown in, death happened in 20 



feconds. (Memoirs on Irritability, pp. 221. 223.) Air, 

 fays Bichat, thrown into the vafeular fyltem, quickly brings 

 on agitation, convulsions, and death. ( Rccherches fur la 

 Vieet la Mort, p. 179.) By forcing air through the wind- 

 pipe into the lung'; with a fyringe, and confining it there, 

 he has made it to enter into the blood-ved'els, winch imme- 

 diately brings on agitation and exertion in the animal ; and 

 if an artery in the leg or foot be now opened, the blood will 

 fpring out frothy, and full of bubbles of air. If hydrogen 

 gas has been ufed, the bubbles may be inflamed ; aiid when 

 this frothy blood has flowed 30 feconds, the actions of life 

 ceafe, and cannot again be reilored, even although frelh air 

 be fupphed. Ibid. 303. Inquiry, § 102, 103. 



If, then, no proof cxift of the palfage of air into the 

 blood by the ordinary courfe of the abforbent veflels, the 

 only other mode of effecting this purpofe that has been 

 hitherto fuggeited, is the power of -chemical affinity. What 

 then are the chemical affinities fubliiling between venal blood 

 and atmofpheric air I About the middle of the 17th cen- 

 tury, Dr. Lower obferved, that the upper furface of venal 

 blood, received into a veffel, acquired a fcarlet colour by 

 expofure to the air ; that if this furface was removed, the 

 fubjacent one was foon changed to the fame colour ; that if 

 the cake of blood, after being allowed to fettle in the veffel, 

 was inverted, its exterior and upper furface fpeedily alfo 

 affumed a florid hue ; and, laltly, that if venal blood was 

 fliaken in a veffel, fo that the air thoroughly intermixed with 

 it, it became entirely florid. (De Corde, p. 178.) Thefe 

 opinions were afterwards held by Sig. Fracaffati and Dr. 

 Slare, the latter of whom obfi , that the blood thrown 

 up by a rupture of the capillary veflels of the luflgS, is 

 frothy and of a fcarlet colour ; the iirlt of which effects lie- 

 attributes to the intermixture of air, and the latter to its 

 tinging power. (Lewthorpe's '. i . . Phil. Tranf. v. iii. 

 p. 235.) Mr. Hewfou employed (imtlar arguments to 

 prove, that the florid colour, acquired by venal blood on 

 expolure, was produced by to atact of the air; and, 

 by injecting air into thejugulai a rabbit, he found 



thai it there alfo rendered the blood ll wid. (Hewfon on 

 the Blood, p. 9.) M. Cigna not only con fin ire- 



going facts, but proved alio that the change of colour in 

 this fluid did not take place when the blood was covered 

 with oil or placed in vacuo ; and Dr. I'j 

 that not only by common air, but more especially by oxj 

 gas this florid colour was produced on the black craila- 



itutn of blood. On Air, v. iii. p. fi 

 In effecting thefe remarkabl "lour ol 



tli- blood, the air itfelf, at the fame time, fullers material 

 ges. Dr. Prieftley found, that in twenty-four ho 



1 g 1 i tr depraved by bein| a ith 



venal hi iod, two of nil 



occupied the fpa ■ I 11 I a half, . ...■-., at the 



beginning ol the cxperui:. ; L v of no 



more than half a mcafure. (I. 



wyi 



