m 



. VII. ANIMAL HEAT. 151 



We have, therefore, no occasion to seek for other sources 

 of animal heat than the chemical processes of respiration 

 and nutrition ; but I think it is an error to attempt to make 

 a rigorous comparison of the results of experiments on ordi- 

 nary combustion produced in a calorimeter, with those 

 which happen in an animal; and to admit, as the source of 

 animal heat, one only of the numerous chemical actions 

 which take place within the same animal. 



In fact, the carbonic acid with which the venous blood 

 is charged, and which is produced by the union of atmos- 

 pheric oxygen with the carbon of the organic elements of 

 the different tissues which become modified, cannot arise 

 from the carbon existing in a free state in these tissues, but 

 in combinations with which we are far from being perfectly 

 acquainted. 



The experiments of Dulong prove that one body com- 

 bined with another does not produce, in burning, or in 

 combining with oxygen, the same amount of heat which it 

 would do if it were employed in its free state. The heat 

 which bicarburetted hydrogen, marsh gas, and oil of turpen- 

 tine, produce, by burning in oxygen, and forming water 

 and carbonic acid, is not equal to, but is generally less than, 

 the amount of heat which would have been furnished, had 

 the volumes of gas composing them been burnt separately. 

 The experiments of Hess and Andrews, which tend to prove 

 that in a given combination, an absolute quantity of heat is 

 developed, whatever may be the condition of the two com- 

 bining bodies, have related solely to the successive com- 

 binations of the same body, as in the case of sulphuric acid, 

 which combines with different numbers of atoms of water. 



If we must limit the explanation of the production of 

 animal heat, exclusively to the chemical combination of 

 carbon and of hydrogen with oxygen, it will be difficult to 

 interpret the results which have been arrived at by Andral 



