ON ANIMAL HEAT. 563 
sorbed by the blood, and conveyed by its circulation to all parts 
of the body. 
But it was urged by the doubters of the correctness of this 
theory, that, if this view was the true one, why was not the blood 
on leaving the lungs exalted in its temperature above what actu- 
ally takes place? To obviate this objection. Dr. Crawford sup- 
posed that arterial blood had a greater capacity than venous 
blood for caloric ; and that the heat so generated in the lungs, 
and imparted to the arterial blood, became latent, and was not set 
free until this blood assumed again its venous character in the 
various parts of the body. The weakness of this course of argu- 
ment was proved by Dr. Davy, who shewed that the capacity of 
the two kinds of blood for caloric was nearly identical. 
26. Some later theorists have imagined that the oxygen which 
the blood extracts from the air is combined with the carbon in 
the course of the circulation, and not in the lungs. This view 
certainly accords with most of the facts noticed, but fails in pro- 
viding sufficiently for the amount of heat acquired by the animal; 
and the general inference, from a most extensive course of experi- 
ments, is, that if the absorption of oxygen be a cause of vital 
heat, it can only be a partial one. “ There must be other sources 
of animal heat besides respiration,” says Muller, (Physiol., 
p. 92.) 
27. To the organic secreting functions have been assigned, by 
some physiologists, an important part in the generation of animal 
caloric. They imagine that, in the different secreting processes of 
the body, the fluids formed having a less capacity for heat than the 
blood from which they are separated, must be the means of render- 
ing sensible heat that was before latent. This position has been 
denied by other examiners, who have failed in detecting the 
necessary difference of capacity for caloric between the secretions 
and the blood from which they are taken. 
28. M. Pouillet supposed he had discovered another source of 
animal heat in the elevation of temperature which occurs on the 
moistening of solid bodies with different fluids. The increase of 
heat said to attend the process of digestion may be given as an 
example illustrative of his views. 
29. As is generally the case when we are at fault in providing 
sufficient cause for any physiological or pathological difficulty, 
the nerves are resorted to in order to mask our ignorance. So in 
this case, some physiologists, despairing of discovering satisfactory 
proof of the source of vital heat, allege that it must consequently 
be nervous. That the temperature of a limb becomes less on the 
division of its nerves is no reason that animal heat should be 
necessarily supplied by nervous action. The section of a nerve 
