4:C6 On the Influence of the Brain 



each expiration ; and hence I was led to believe, that ths 

 respiratory function was performed nearly as under ordinary 

 circumstances, and that the usual chemical changes were 

 produced on the blood. It appeared, however, desirable to 

 obtain some more accurate knowledge on this point, and 

 I have therefore instituted a series of experiments, for the 

 purpose of ascertaining the relative quantities of air con- 

 sumed in breaihing, by animals in a natural state, and by 

 animals in which the brain has cea>ed to perform its office, 

 and I now have the honcmr of communicating an account 

 of these experiments to the Society. 



It has been shown, by Messrs, Allen and Pepys, first, 

 that every cubic inch of carbonic acid requires exactly a 

 cubic inch of oxygen gas for its formation* ; secondly, that 

 when respiration is performed by a . warm-blooded animal 

 in atmospheric air, the azote remains unaltered, and the 

 carbonic acid exactly equals, volume for volume, the oxygen 

 gas which disappearsf. 



There is thertfore reason to believe, that the watery va- 

 pour, which escapes with the air in expiration, is not 

 formed from the union of hvdrogen uith oxygen in the 

 lungs, but that it is exhaled from the mucous membrane 

 of the mduth and pharynx, resembling the watery exhala- 

 tion which takes place tram the peritonaeum, or any other 

 internal surlace when exposed ; and this conclusion appears 

 to be fully confirined by the experiir>ents of M. Magendie, 

 lately communicated to the National Institute of Pans. 



These circumstances are of importance in the present 

 communication, which they render more simple, as they 

 show, that in order to ascertain the changes produced on 

 the air in respiration, it is only necessary to tind the quan- 

 tity of carbonic acid given out from the lungs. This be- 

 comes an exact measure of the oxygen consumed, and the 

 azote of the air and the watery vapour expired need not be 

 taken into the account. 



For the purpose of examining the changes produced on 

 the air, by an-mals breathing under the diflerent circum- 

 stances above mentioned, I contrived the apparatus which 

 is represented in the annexed Plate. 



Description nf the Jpparattis. (Plate XI.) 



A. Is a wooden stand, in which i< a circular gi;oove | of 

 Jin inch in depth, and the same in width. 



B. Is a bell-glass, the rim ol which is received in the 



• Phil. Trans. 1807, part ii. 

 t Phil. Trans. 180S, part ii. Ibid. 1S09, part ii. 



circular 



