18 On Respiration and Animal Heat. 
never so much as conjectured by any one prior 
to him. 
According to this theory, the acquisitior 
and distribution of animal heat is obvious = 
In respiration, heat is abstracted from the at- 
mospheric air, or more properly, from the 
oxygenous part of it inspired, in consequence 
of the chemical union of elements; this heat 
is imparted to the blood without materially 
affecting its temperature, and is, during the 
course of circulation, given out to the rest of 
the body, im proportion as the blood changes 
from its arterial to its venous constitution. 
Most, if not all, philosophers who have at- 
tended to this subject since, have adopted the 
two fundamental positions above laid down, 
which have never, E believe, been controverted 
by any one; and, whilst they continue to be 
admitted, it would be in vain to frame any 
other theory in order to account for animal 
heat. 
» Notwithstanding this general agreement as 
to the source of animal heat, there are still 
various opinions respecting the mode of 
those chemical changes that take place in 
the air and in the blood in consequence of 
respiration. Before we can animadvert upon 
these, it will be necessary to premise, that the 
air of the atmosphere inspired consists of 
