SECT. II. PHYSIOLOGY. 11 
of bellows to the trachea, by which means he 
carried on its respiration and circulation for an 
hour and a half; a thermometer placed in the 
thorax, stood at 86°. Another rabbit, of the same 
size and colour, had its circulation stopped by the 
application of a ligature to the base of the heart ; 
and at the end of an hour and a half, the heat 
of its thorax was 884°. Mr. Brodie repeated these 
experiments frequently, from which he draws the 
general conclusion, that “ when the air respired is 
colder than the natural temperature of the animal, 
the effect of respiration is not to generate, but 
diminish animal heat.” If physiology, like the 
other sciences, is to be founded on facts, it is 
impossible to dissent from Mr. Brodie’s conclusion: 
the pneumatic theory must therefore necessarily 
be abandoned, and recurrence made to the 
antiquated doctrine of Hippocrates, Philiston, and 
Diocles, who regarded respiration as a ventilation 
of the innate heat. 
x. The mathematical physiologists alleged, that 
the motion of the blood is a source of animal heat; 
but this notion is contested by Mr. Hunter, than 
whom there is no more powerful advocate for 
the influence of the blood in general. “ Animal 
heat (says this distinguished author) does not 
depend on the motion of the blood; the nose of 
the dog, which is always nearly of the same heat 
in all temperatures of the air, is well supplied 
