380 Mr. Brodie’s Experiments and Observations 
the union of hydrogen with oxygen in the lungs, but that it is 
exhaled from the mucous membrane of the mouth and pha- 
rynx, resembling the watery exhalation which takes place 
from the peritonaeum, or any other internal surface when ex- 
posed ; and this conclusion appears to be fully confirmed by 
the experiments of M. Magendie, lately communicated to the 
National Institute of Paris. 
These circumstances are of importance in the present com- 
munication, 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 find the quantity of carbonic 
acid given out from the lungs. This becomes an exact mea- 
sure 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 animals breathing under the different circumstances 
abovementioned, I contrived the apparatus, which is repre- 
sented in the annexed Plate. 
Description of the Apparatus. 
A. Is a wooden stand, in which is a circular groove f of an 
inch in depth, and the same in width. 
B. Is a bell-glass, the rim of which is received in the circular 
groove of the wooden stand. In the upper part of the bell- 
glass is an opening, admitting a tube connected with the 
bladder C. 
D. Is a bottle of elastic gum, having a brass stop-cock E 
connected with it. 
F. Is a silver tube, of which one end is adapted to receive 
the tube of the stop-cock E, while the other extremity, making 
