10 ANALYTIC SECT. II. 
material difference between venous and arterial 
blood, in respect to specific caloric, excepting what 
arises from difference of specific gravity.” Dr. 
Crawford erred also in supposing, that an estimate 
of the calorie produced by chemical combinations 
can be made from the capacity of the new pro- 
duction. Professor Dulong of Paris, has lately 
observed, that in the chemical combination of two 
bodies, a vast quantity of calorie may be disenga- 
ged, and the capacity of the resulting compound 
remain about the mean capacity of the two ingre- 
dients. Dr. Crawford’s calculation of the quantity 
of caloric generated during inspiration, is there- 
fore altogether conjectural; his conclusions, con- 
sequently, are unworthy of implicit credit. It may 
further be objected to the pneumatic theory of ani- 
mal heat, that supposing it to be caused by respira- 
tion, the degree of heat ought always to correspond 
with the quantity of air respired; whereas an in- 
dividual may respire during* digestion one-fourth 
greater quantity of oxygen than before a meal, 
and the animal temperature not vary one degree. 
1x. Forcible as these objections may appear 
against the pneumatic theory, Mr. Brodie has the 
honour of having effected the most conclusive 
refutation of it: he divided the spinal marrow of 
a rabbit, tied its carotid arteries, and fixed a pair 

* Vide Lavoisier and Seguin. 
