42 On Respiration and Animal Heat. 
how far the above circumstances might be connected with 
the function of respiration. We found that each of us 
breathed at an average 20 times in a minute, but that the 
quantity of air which he expired each time, was only two 
thirds of that which I expired. The capacities of our 
lungs appeared to be in the same ratio of 2 to 3; for, the 
whole quantities of air which each of us could expel from 
our lungs, both after a natural and forced inspiration, were 
as nearly as we could determine in that ratio. The quality 
of the air expired by us was found to be the same, both in 
the natural and foreed expirations; in the former case the 
air contained 43 per cent. of carbonie acid, and 16 of 
oxygen, and in the latter, 7 carbonic acid, and 13 or 14 
oxygen. The size of our persons is nearly the same. The 
experiments were made in August, in a temperature of 60°, 
Now if the quantity of heat generated, or more properly 
speaking, acquired by the animal system, be in direct pro- 
portion ta the carbonic acid expired from the lungs, as all 
experience would seem to warrant from its evolation, the 
above results are consistent therewith, 2nd the facts admit 
of a satisfactory explanation. 
a 
Ihave Just seen a paper in the Philosophical Transactions 
for the present year (1811), by Mr. Brodie, containing 
some facts affecting the theory of animal heat. It is en- 
titled “ Physivlogical Researches respecting the Influence 
ef the Brain on the Action of the Heart, and on the Ges 
neration of Animal Heat.” There is an important addi- 
tion to it in a subsequent paper of the same author. 
From his experiments the author deduces the following 
conclusions: 
“1. The influence of the brain is net directly necessary 
to the action of the heart. 
