262 PRINCIPLES OF ANIMAL NUTRITION. 
The first part of this hypothesis was readily susceptible of verifi- 
cation by a quantitative determination of the oxygen taken up and 
the carbon dioxide given off, but the second portion was too bold to 
secure general acceptance. Lavoisier, therefore, with the aid of 
Laplace, subsequently attempted to secure experimental evidence 
as to its truth. To this end they determined the amount of heat 
given off by a guinea pig in an ice-calorimeter, while in a second 
experiment the animal was placed under a bell-jar and the produc- 
tion of carbon dioxide determined. Having previously determined 
by means of the ice-calorimeter the heat of combustion of carbon, 
the results of these two trials gave them data for comparing this 
amount with that produced by the animal. The computed amount 
of heat was 25.41 Cals.; that produced by the animal 31.82 Cals. 
Several sources of error were inherent in the experimental 
methods adopted, of some of which Lavoisier was aware, which 
tended to make the computed amount of heat too small. Taking 
these into consideration, Lavoisier considered that the experiment 
substantially confirmed his hypothesis. 
At about the same time Crawford * was investigating the same 
subject, and while his methods were rather primitive and his results 
less accurate than those of Lavoisier and Laplace, his general con- 
clusions were the same. Of later experiments may be mentioned 
especially those of Despretz + and of Dulong.{ Both investigators 
employed very similar apparatus, viz., a water-calorimeter through 
which a current of air was passed, the respiratory products and the 
heat being determined in the same experiment. The proportion of 
the oxygen consumed which united with hydrogen was also deter- 
mined. Both investigators found more heat than they could ac- 
count for by the oxidation of tissue and concluded that chemical 
action is the chief but not the only source of animal heat.§ 
With the advance of physiological knowledge and the recogni- 
tion of the multiplicity and complexity of the processes taking place 
in the body, the combustion theory of the origin of animal heat 
lost rather than gained ground. A few clear-sighted physiologists 
* Experiments and Observations on Animal Heat, 1788. 
¢ Ann. de Chim. et de Phys. (2), 26, 337. 
t Ibid. (3), 1, 440. 
§ Compare Liebig’s discussion of their experiments, Thierchemie, p. 28. 
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