16 On Respiration and Animal Heat. 
consisted of carbonic acid gas; this fact, when 
joined to the former, led to the discovery of 
the true cause of animal heat, or that excess 
of temperature which warm-blooded animals 
possess, above the temperature of the sur- 
rounding atmosphere. 
The striking analogy which the effects of 
respiration have to those of the combustion of 
charcoal, could not long escape the observa- 
tion of Lavoisier and others. In both cases, 
charcoal, in a fixed or melastic state, combines 
with oxygen, and produces carbonic acid gas. 
In combustion, a great quantity of heat is 
liberated, so as to raise the temperature of 
surroundmg bodies to an intense degree; in 
respiration, however, little or no increase of 
temperature is observed, if we except the air 
itself, which is inspired cold and expired 
warm. This want of complete resemblance 
in the chemical effects of combustion and re- 
spiration, for a time, obstructed the progress 
of this branch of physiology. It was perceived 
that the quantity of carbonic acid produced 
by respiration, had it been obtained from the 
combustion of charcoal, would have evolved 
heat sufficient to preserve the temperature of 
the body; but the heat so evolved, if applied 
to the lungs of an animal, must be injurious, 
if not fatal. The body of a living animal is 
