RESPIRATION. 



in declaring it, as our decided opinion, that the experiments 

 leaft liable to error, molt carefully performed, and therefore 

 deferving our greateft confidence, are thofe which contradict 

 the notion of an abforption of oxygen. 



" In cafes," fays Mr. Ellis, " where lb many caufes concur 

 to render the apparent bulk of acid lefs than it ought to be, 

 and lefs than that of the oxygen loll, it is furely more rea- 

 fonable to give greater credit to thofe refults, which indicate 

 an equality of volume between thefe gafes, than to thofe 

 which declare a difference ; iince the former not only go 

 with the latter to the fulleft extent ; but, purfuing the fame 

 track, have actually gone beyond them, and thereby reached 

 a point, which the others have been unable to gain. In fact, 

 to prefer thofe experiments, which indicate a difference, to 

 thole which prove an equality of volume, would be not only 

 to halt in our progrefs, but to make a retrograde movement, 

 and thus to fuffer a negative inference to outweigh a pofi- 

 tive proof." Further Inquiry, p. 279. 



By the experiments of Mell'rs. Allen and Pepys, we have 

 feen it proved, that when a guinea pig breathes a given 

 itity of air in 3. natural manner, no variation whatever 

 obft rvcd in the bulk of that air ; and that in man, in 

 whom many caufes, not affecting the lower animals, contri- 

 bute to produce error, when the refpiration was nearly na- 

 tural, the general average of the deficiency, in the total 

 amount of common air infpired, was only about fix parts in 

 1000, and in one inltance confiderably lefs than two. The 

 imallnefs of this deficiency, fay thefe chemilts, furprifed us 

 very much ; and it probably arifes from the difficulty, or, 

 as they elfewhere term it, the impoffibility of always bring- 

 iag the lungs to the fame ilate after forcible expiration. 



Under other circumftances, as in the experiment recited 

 above, of refpiration continued until the operator became 

 inienlible, thefe gentlemen conceive that oxygen is abforbed. 

 To this inference, fays Mr. Ellis, as far as it regards what 

 is here called an abforption of oxygen, we mult beg leave 

 to object. That the united volumes of oxygen and carbonic 

 acid expired were lefs than the total volume of oxygen in- 

 ipired, we readily grant ; but we deny that this fad affords 

 any adequate proof of an abforption of this latter gas. To 

 the chemift, indeed, the mere fact of the difappearance of 

 a portion of oxygen may fupply fufficient evidence of its 

 abforption, in the fenl'e in which he may choofe to employ 

 that term ; but the phyfiologiit farther requires to know, 

 by what organs or veffels it is removed, in what courfe it is 

 conveyed, and what ufes it is deftined to ferve. On none of 

 thefe points, however, does he gain any information ; and 

 all the anatomical knowledge which he poffeiles of the Itruc- 

 tu-.-e of the lungs, and of the properties of the living ab- 

 forbent fyftem, is adverfe to fuch a doarine. Should he 

 apply to the chemitt for a folution of his difficulties, he is 

 told that oxygen does not chemically combine with other 

 bodies, unlefs it be brought into actual contact with them ; 

 and he knows, that, in the prefent cafe, this contact is im- 

 poffible, becaufe the membranes, both of the air-cells and 

 blood-veffels, are interpofed between the air and the blood 

 in the lungs. Even it, contrary to all experience and ana- 

 logy, he were to concede to the chemift the exiftence of 

 pores or other paffages in the cells and blood-vefTels, through 

 which this oxygen might be attrafted and combine with the 

 bloody he is equally embarraffed to difcover the reafon or 

 mode in which it is again fo fpeedily expelled, or what ufe. 

 ful purpofe it can ferve, fince no portion of it is permanently 

 retained. The fcience of chermitry furnifhes no example 

 of fimilar operations,— of fluids which attract gafes and 

 combine them, fo as to reduce their elafticity, and then, 

 without any apparent change of condition or circum- 



ftances, almoft inftantly difcharge then, in a new and elaftic 

 form. 



If, farther, we compare the refults of the two feries of 

 experiments made by Melirs. Allen and Pepys, the difficul- 

 ties, in a phyliological point of view, greatly accumulate 

 upon us. For, if an abforption of oxygen real'ly take place 

 in the lungs, how does it happen, that, in the firlt thirteen 

 experiments, made with feveral thoufand cubic inches of air, 

 and which occupied from ten to twenty.four minutes of 

 time, a very fmall loft in the whole bulk of air, and not the 

 fmalleft in its proportion of oxygen, occurred ; while, in 

 two other experiments, made with only 300 inches of air, 

 and continued only for three minutes of time, a great de- 

 ficiency in the whole bulk of air, and a lofs of one-third of 

 its oxygen, took place. In all thefe experiments, except 

 the twelfth, in which, inftead of lofs, there was actually an 

 increafe of eleven cubic inches upon the bulk of air refpired 

 (Phil. Tranf. 1S0S, p. 256.), tie fame perfon appears to 

 have breathed, and the air was of fimilar compofition. Con- 

 fequently, the caufe of variation in the refult is to be fought, 

 not in any difference in the ar.imal organs, or in the original 

 compofition of the air, but, probably, in fome circum- 

 (tances of dillimilarity, which accompanied the progrefs of 

 the experiment. 



Now the bare ftatement of facts points out a great diffi- 

 nulirity, not only in the chemical refults, but in the circum- 

 ftances accompanying the experiments, and in the effects 

 which they produced in the fyftem. For in the firft thirteen 

 experiments, wliich occupied from ten to twenty-four mi- 

 nutes, and in which no lofs of oxygen occurred, the air 

 was only once pafTed through the lungs, the breathing was 

 nearly natural, the operator fcarcely fatigued, and his pulfe 

 not railed more than about one beat in a minute. (Ibid. 253.) 

 But in the two experiments in wliich oxygen is faid to be 

 abforbed, the fame air was palled eight or ten timet through 

 the lungs ; and, in lefs than a minute, the operator found 

 himfelf obliged to take deeper and deeper infpirations. At 

 laft, the efforts to take in air became very ftrong and fudden, 

 with a great fenfe of oppreflion and fuffocation in the cheft, 

 indiftinct vilion, buzz in the ears, lofs of recollection, and, 

 at the end of three minutes, perfeft infenlibility. (Ibid. 

 260 — 262.) This difference in the effects produced in the 

 fyftem, we do not heiitate to afcribe to a difference in the 

 compofition of the air, which, in the firft experiments, was 

 refpired in a natural ftate, but, in the two lalt, by repeated 

 breathing, was rendered more and more unfit to carry on 

 refpiration, until, at length, its power of fupporting that 

 function altogether ceafed. 



But becauie under circumftances, in which the mental and 

 a.-.imal powers were in complete abeyance, the refpiratory 

 organs were not able to make fo complete an expulfion of 

 the infpired air as they effect in tkeir natural ftate of health 

 and vigour, are we, therefore, entitled at once to conclude, 

 that all the air which was not expelled was really alfarc 

 Setting afide the anatomical difficulties in the cafe, let us, 

 for a moment, look only to the chemical confequences, to 

 wluch fuch a conclufion would conduct us. If the mere 

 difappearance of any gas, received into the lungs, be fuf. 

 ficient evidence of its abforption, then every gas, which is 

 not returned, muft be held to be abforbed, Are we then 

 prepared to admit that hydrogen and nitrogen gafes are ab- 

 forbed by the blood ? for, when their refpiration is carried 

 to its full exteut, they, too, equally difappear. This fup- 

 pofed abforption, however, cannot proceed from the opera- 

 tion of chemical attraction, for little or no affinity fubfifts. 

 between thefe gafes and the blood. Neither can it arife 

 from the operation of the living fyftem ;■ for it occurs only 

 3 when 



