372 
y 
medium (178.), its permanence can be secured only 
by the constant exercise of some necessary animal 
function. But no function which the animal exerts, 
except that of respiration, can be conceived thus to 
afford a constant supply of heat ; and since, in the 
exercise of this function, the oxygen gas of the air is 
uniformly converted into carbonic acid, under which 
its latent caloric is necessarily set free, the liberation 
of this caloric by the perpetual decomposition of the 
air (180.) must be regarded as the natural and ne- 
cessary means by which the animal temperature is 
sustained. 
685. In the higher classes of animals, which pos- 
sess a temperature greatly exceeding that of the sur- 
rounding medium, and which, under every vicissi- 
tude of heat and cold, preserve nearly an uniform 
degree of heat, we have referred the primary source 
of animal temperature to a similar extrication of ca- 
loric, arising from the decomposition of the air (189.), 
in the exercise of the respiratory function, as origi- 
nally suggested by the illustrious Dr Black, and sub- 
sequently developed and confirmed by the elaborate 
researches of Dr Crawford. In support of this doc- 
trine, it has been maintained, that the latent heat of 
the air is necessarily set free in the lungs (190.) 
during the exercise of the respiratory function ; that 
the blood, after this extrication of caloric, possesses 
an increased portion (191.) of specific heat ; and that 
the quantity of caloric thus actually afforded to that 
fluid may be considered sufficient (192. 3.) to account 
for the height and continuance of animal tempera-. 
ture. 
