254 PRINCIPLES OF ANIMAL NUTRITION. 
change is brought about by what is, in effect, a process of oxidation 
simply. That many other chemical processes take place in the 
body is, however, well known, and Berthelot * in particular lays 
special stress upon the possibility of numerous cleavages, syntheses, 
hydrations, and dehydrations in which the respiratory quotient 
may vary between wide limits and in which the heat production is 
not necessarily proportional to either the oxygen consumed or the 
carbon dioxide generated. An example of such a process is the 
formation of fat from carbohydrates, which, as we have seen, may 
be regarded in the light of an intra-molecular combustion in which 
no oxygen from outside is consumed, but in which there is an evolu- 
tion of heat. As an illustration of the opposite possibility—an 
evolution of heat without production of carbon dioxide—Berthelot 
instances ¢ the oxidation of a molecule of ethyl alcohol by suc- 
cessive atoms of oxygen to ethyl aldehyde, acetic acid, glycollic 
acid, oxyglycollic acid, oxalic acid, and finally carbon dioxide and 
water. Only in the last of these stages is there an evolution of 
carbon dioxide, yet in each stage there is an evolution of heat vary- 
ing from 39.9 Cals. to 73.3 Cals. per atom of oxygen. 
But while the possibility and even probability of similar reac- 
tions in the body of the animal cannot be denied, it certainly 
seems very questionable, in the light of the results to be considered 
in the next chapter, whether they have any material bearing upon 
the determination of the general balance of energy. We know at 
least approximately the final products of metabolism, and accord- 
ing to the law of initial and final states (p. 228) the intermediate 
reactions can only affect the total amount of energy liberated in 
case some of the intermediate products are retained in the organism. 
The only material which we know to be stored up in any consider- 
able quantity in the normal body, however, is fat, and the amount 
of this we can at least approximately determine. It is of course 
possible that in an experiment covering a few minutes only, these 
intermediate reactions may seriously affect the result, but in an 
experiment covering several hours or a whole day we can hardly 
conceive such to be the case. Indeed we may probably go still 
further. It seems to be a general physiological law that the func- 
tions of the organism are adjusted to a certain average composition 
* Chaleur Animale, Part I. } Loc, cit., p. 44. 
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