Dissertation on Animal Heat. 177 
heating stove. It was easy to make sure of the real state of the 
fact, by introducing a thermometer into the thorax of a living ani- 
mal. The experiment was made, and scarcely any greater degree 
of heat was observed. 
It was at first endeavoured to explain this contradiction by 
supposing that all the caloric which is separated from the air is 
absorbed in order to gasify the carbonic acid and evaporate the 
water, a supposition which many foreign physiologists still ad- 
mit, although it is known that carbonic gas becomes condensed 
with scarcely any elevation of temperature, and may also be gasi- 
fied without absorbing almost any heat, and that the ordinary 
temperature of bodies with the aid of the suspending affinity of 
the air is more than sufficient for the evaporation of water, as is 
proved by cutaneous transpiration, and other evaporations which 
are produced by natural heat alone. 
Abandoning therefore this theory, which did not besides furnish 
any reason for the uniform distribution of animal heat, nor ex- 
plain, any more than the experiments opposed to it, the origin 
of that heat, another was had recourse to, but equally unsatisfac- 
tory—I allude to the theory of changed capacities. 
I should have passed over this theory also without observation, 
if it had not been in our own days revived in all its original purity 
by men of merit, and if physiologists of the first rank had not 
united it with the theory of combustion. 
This theory supposes between the venous and arterial bloods a 
great difference of capacity, in virtue of which the latter takes up 
and combines, without any rise of temperature, the whole quan- 
tity of caloric which is set free by the combustion of carbon and 
the hydrogen of venous blood, and it founds this supposition on 
the medium of the caloric contained in the two bloods, and of the 
air inspired and inhaled. 
As this difference of capacity depends on the different nature 
of the two bloods, it ought to change in proportion as by the ef- 
fect of circulation the arterial blood approaches to the nature of 
the venous blood, and it ought to resolve itself in the same de- 
gree with the caloric which spreads itself uniformly through all 
parts of bodies. | 
This theory, which seems to remove the two great difficulties 
of the theory of direct combustion, the permanence of the tem- 
perature of the cavity of the thorax, and the equal distribution 
of heat, is however contradicted by many facts, as we shall now 
proceed to prove. 
In the first place, nothing establishes this change of capacity 
which the venous blood is supposed to undergo in becoming ar- 
terial blood ; and it is far from probable that so slight a change 
Vol, 53, No. 251. March 1819. M in 
