382 Mr. Erodie’s Experiments and Observations 
two or three times, and the air in the bottle was then preserved 
for examination. The proportion of carbonic acid being ascer- 
tianed, and the capacities of the different parts of the apparatus, 
and the space occupied by the animal being known, the total 
quantity of carbonic acid formed, and consequently of oxygen 
consumed, was easily estimated. 
When the experiment was made on an animal, in whom 
the functions of the brain were destroyed, and in whom there- 
fore voluntar}' - respiration had ceased, the narrow extremity 
of the tube was inserted into an artificial opening in the tra- 
chea, and the animal being placed under the bell-glass, the 
lungs were inflated at regular intervals, by means of pressure 
made on the gum-bottle. The tube being smaller than the 
trachea, the greater portion of the air in expiration escaped by 
the side of the tube into the general cavity of the bell-glass, 
while the gum- bottle filled itself by its own elasticity with 
air through the opening G. At the end of the experiment, 
a portion of air was preserved for examination, and the quan- 
tity of carbonic acid was estimated in the way already de- 
scribed. 
The animals employed in these experiments were of the 
same species, and nearly of the same size. Attention to these 
circumstances was judged necessary, that the results might 
be as conclusive as possible. The chemical examination of the 
air was made by agitating it in a graduated measure over 
quicksilver, with a watery solution of potash. My friend Mr. 
Brande gave me his assistance in this part of the present 
investigation, as he had done on many former occasions. It 
will be observed, that in estimating the proportion of car- 
bonic acid, no allowance has been made for that contained in 
