Hoj/al Society. 1 i I 



May 21. — 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 resumed 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 

 erroneous 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 j 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 

 with oxygen gas, in place of atmospheric air, were attended with the 

 like results, but in a more striking degree $ and tend therefore to 

 corroborate the views entertained by the author of the theory of re- 

 spiration. According to these views, it is neither in the lungs, nor 

 generally in the course of the circulation, but only during its passage 

 through the capillary system of vessels, that the blood undergoes the 

 change from arterial to venous j a change consisting in the formation 

 of carbonic acid, by the addition of particles of carbon derived from 

 the solid textures of the body, and which had combined with the oxy- 

 gen supplied by the arterial blood : and it is by this combination that 



[* See Prof. Graham on the law of the diffusion of gases, Lond. and 

 Edmb. Phil. Mag., vol. ii. p. 3f>4.— Edit.] 



