334 



trate in considerable quantity ; this Mr. Faraday conjectures to have 

 been saltpetre, which had been added to the water by the priests. 



The reading of a paper was commenced, entitled, " Observations 

 on the Theory of Respiration." By William Stevens, M.D., D.C.L., 

 Fellow of the Royal College of Physicians of Copenhagen, and of 

 Surgeons of London. Communicated by W. T.Brande, Esq., V.P.R.S. 



May 21, 1835. 



WILLIAM THOMAS BRANDE, Esq., Vice-President, in the Chair. 



The reading of the paper, entitled, " Observations on the Theory 

 of Respiration." By William Stevens, M.D. D.C.L., Fellow of the 

 Royal College of Physicians of Copenhagen, and of Surgeons of 

 London. Communicated by W. T. Brande, Esq., V.P.R.S., was re- 

 sumed and concluded. 



From the fact that no carbonic acid gas is given out by venous blood 

 when that fluid is subjected to the action of the air-pump, former 

 experimentalists had inferred that this blood contains no carbonic 

 acid. The author of the present paper contends that this is an er- 

 roneous inference ; first, by showing that serum, which had been 

 made to absorb a considerable quantity of this gas, does not yield it 

 upon the removal of the atmospheric pressure ; and next, by addu- 

 cing several experiments in proof of the strong attraction exerted on 

 carbonic acid both by hydrogen and by oxygen gases, which were 

 found to absorb it readily through the medium of moistened mem- 

 brane. By means of a peculiar apparatus, consisting of a double- 

 necked bottle, to which a set of bent tubes were adapted, he ascer- 

 tained that venous blood, agitated with pure hydrogen gas, and al- 

 lowed to remain for an hour in contact with it, imparts to that gas 

 a considerable quantity of carbonic acid. The same result had, in- 

 deed, been obtained, in a former experiment, by the simple applica- 

 tion of heat to venous blood confined under hydrogen gas ; but on 

 account of the possible chemical agency of heat, the inference drawn 

 from that experiment is less conclusive than from experiments in 

 which the air-pump alone is employed. The author found that, in 

 like manner, atmospheric air, by remaining, for a sufficient time, in 

 contact with venous blood, on the application of the air-pump, ac- 

 quires carbonic acid. The hypothesis that the carbon of the blood 

 attracts the oxygen of the air into the fluid, and there combines with 

 it, and that the carbonic acid thus formed is afterwards exhaled, ap- 

 pears to be inconsistent with the fact that all acids, and carbonic 

 acid more especially, impart to the blood a black colour ; whereas 

 the immediate effect of exposing venous blood to atmospheric air, or 

 to oxygen gas, is a change of colour from a dark to a bright scarlet, 

 implying its conversion from the venous to the arterial character: 

 hence the author infers that the acid is not formed during the expe- 

 riment in question, but already exists in the venous blood, and is ex- 

 tracted from it by the atmospheric air. Similar experiments made 



