RES PI RATION. 



are placed in contact, do not prove an attraction and dif- 

 fulion of air through the blood ; but fhew only that a re- 

 ciprocal action takes place, by which a new product is 

 formed : no inference, therefore, in favour of an attraction 

 of air by the blood in the lungs, can be drawn from the 

 reciprocal action which they exert on each other out of the 

 body. Inquiry, § 96 — 100. 



It is, farther, an objection to this fuppofed operation of 

 oxygen, that in the lungs the blood and air do not come 

 into contact:, and therefore although the combination of 

 oxygen with that fluid might be conceived to happen, when 

 they arc placed together out of the body, yet the interven- 

 tion of organifed membranes may be fuppofed to prevent 

 fuch an union in the living fyftem. In the ordinary opera- 

 tions of chemiUrv, fuch an interpofition of animal fub- 

 itance would be confidered fufficient to vitiate the refult of 

 any fimilar experiment in which it was employed ; but in 

 the application of this fcience to the living body, neither 

 membranes nor blood-vellels are conceived to oppofe any 

 obftacle to the exertioit of chemical action, or, in the 

 fmallell degree, to affect its refult. In fupport of this 

 fuppofed operation of oxygen on the blood, lome experi- 

 ments of Dr. Prieltley have been appealed to, as affording 

 decifive evidence that this fubitance has the power of pene- 

 trating a compact membranous body, and may, confe- 

 quently, penetrate the cells and blood-veffels of the lungs. 

 The importance, which has been attached to thefe experi- 

 ments, in all the late hypothefes which have been propofed 

 to explain the function of refpiration, renders it necefl'ary 

 for us to examine them with fome minutenefs, in order to 

 difcover the true relation which they bear to the prefent 

 queftion. 



Dr. Prieftley, who, as we fhall hereafter fee, fuppofed 

 that venal blood became red by imparting its phlogifton to 

 the air, knew well that the blood in the lungs was feparated 

 from the air by a membranous fubitance, which, however, 

 according to Dr. Hales, does not in thicknefs exceed the 

 ■nrVirth part of an inch. To afcertain the effect of this 

 circumdance, he put fome black blood into a bladder 

 moiitened with a little [brum, and then tying the bladder 

 very clofe, he hung it in a free expofure to the air. The 

 next day, all the lower furface of the blood, which had 

 been feparated from the air by the intervention of the 

 bladder, had acquired a coating of a florid red colour, as 

 thick, it appeared, as it would have acquired, if it had 

 been immediately expofed to the open air ; fo that this 

 membrane had been no impediment to the aftion of the air 

 on the blood. This experiment was repeated, without 

 previoufly moiltening the bladder, and with the very fame 

 refult. Obf. on Air, vol. iii. p. 369. 



Blit although in thefe experiments the blood was ren- 

 dered red by the agency of the air, yet we are not entitled 

 to conclude, that this rednefs was produced by the combina- 

 tion of its oxygen, unlefs we can (hew, not only that this 

 fubitance comes into contact with the blood, but is likewife 

 capable of changing it to a red colour. Dr. Prieftley 

 himfelf, who believed the blood to become red by the lots 

 of phlogillon, could draw no fuch conclufion ; and it is 

 not a little remarkable that this philolopher, who had be- 

 fore fo well obferved the reciprocal effects produced in the 

 air, when it thus changed the colour of the blood (lor. 

 cit. p. 336.), fhould in thefe experiments bave entirely 

 overlooked them. It is (till more remarkable, fince thefe 

 experiments have drawn fo much attention, and feem now 

 to be the chief or only remaining evidence urged in fup- 

 port of the hypothecs of oxygenation, that fome attempt 

 has not been made to inquire farther into the actual cireum- 



Vol. XXX. 



itance6 which attend them. It is this examination w 

 ue now propofe to make, in the hope, that if it do not lead 

 us to a knowledge of the true caufc of this phenomenon, 

 it may at leaft ferve to fhew to what it is not to be 

 afenbed. 



With this view, we procured a quantity of black blood, 

 and putting it inco a fheep's bladder, fufpended it from the 

 top of a jar containing about 100 cubic inches of atmo- 

 fpheric air. The jar was inverted in a faucer containing 

 mercury, and within it a fmall cup of folution of potaffa 

 was likewife placed. The blood, in a fhort time, affumed 

 a florid hue, and a dimnefs extended over the infide of the 

 jar. By the next day, the mercury in the faucer had rifen 

 ,v ths of an inch into the jar, and it continued to rife feveral 

 days ; fo that by the fifth day it had reached nearly to an 

 inch in height. The jar was then raifed, and diluted acid 

 being poured upon the alkaline folution, difengaged from 

 it a large quantity of carbonic acid gas. By this experi- 

 ment, therefore, we are taught, that, when black blood 

 allumes a red colour by being thus placed in a moiftened 

 bladder, and expofed to atmofpheric air, the air itfelf, at 

 the fame time, undergoes a change ; for its volume is dimi- 

 nifhed, and carbonic acid is produced. 



To afcertain thefe facts with greater precifion, we put 

 another quantity of black blood into a fmall bladder, and 

 fufpended it, as before, from the top of a final] jar inverted 

 in mercury, and which contained 18.3 cubic inches of 

 atmofpheric air. Under this jar alfo a fmall cup of 

 folution of potafla was placed. The blood, as before, 

 was foon reddened, and the jar became dim. In two 

 days, the mercury had rifen nearly half an inch into the 

 jar, and by the clofe of the fourth day, it flood feven- 

 eighths of an inch high, where it remained for fome time 

 quite flationary. On analyfing the refidual air, it was 

 found to fuffer no change, either from agitation with lime- 

 water, or by being expofed to the contact of phofphorus ; 

 fo that, though all the oxygen had difappeared, no carbonic- 

 acid was prefent, but that gas was entirely attracted by the 

 water of potaffa employed. 



The capacity of the jar, in the above experiment, has 

 been ftatcd to be equal to 18.3 cubic inches ; and the 

 bladder, with its contents, together with the cup and folu- 

 tion, we found to occupy a fpace equal to 5.2, which re- 

 duces the actual bulk of air, employed in the experiment, 

 to 1 3. 1 cubic inches. The mercury which in eonfequence 

 of the attraction of the carbonic acid had rifen feven-eighths 

 of an inch into the jar, occupied a fpace equal to three 

 cubic inches ; fo that of the 13. 1 inches of air originally 

 employed, three had difappeared, and -, J , = r ,' ,, or a por- 

 tion of the air, was thus converted into carbonic acid, 

 which comes very near to the proportion of oxygen gas 

 which the atmotphcre is known to contain. Hence we 

 infer, that, in this experiment, all the oxygen gas that 

 difappeared was converted into carbonic acid ; and con. 

 fequ'ently we deny that any oxygen penetrated the bladder, 

 in order to combine with the blood. 



As thus it is denied that the blood, in thefe experiments, 

 received any ponderable matter from the air, fo likewife it 

 will appear t from the facts which follow, that the air re- 

 ceives no Inch matter from the blood. We tilled bladders 

 with water, and fufpended them i:i jars o{ atmofpheric air, 

 in the manner defcribed above ; and found that the oxygen 

 gas of thi< air was converted into carbonic acid, in the fame 

 manner aa when the bladders were filled with blood : and if 

 the experiment was continued a fufficient length of time, 

 the whole of the oxygen gas was, in like manner, made to 

 difappear. The fame effects followed from the introduction 

 'I of 



