THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 153 
oxidized liberates but about 4.2 Cals. The relative values of fat 
and starch, then, are as 9.5:4.2 or as 2.26:1. Similarly, one 
gram of proteids oxidized to carbon dioxide, water, and the nitrog- 
enous metabolic products of feces and urine liberates (in the dog) 
about 4.4 Cals. of energy. So far, therefore, as they are used as 
a source of energy simply and not for constructive purposes, their 
value, compared with starch, would be as 4.4 : 4.2 or as 1.05: 1. 
A rival theory of “isoglycosic values,” the basis of which has 
already been indicated in Chapter lI, has been advanced by Chau- 
veau * and his school in Paris. According to this school, dextrose 
(or glycogen) constitutes the material which is consumed in the 
vital activities of the organism. The various nutrients, then, will 
be of value to the organism in proportion to the amount of gly- 
cogen or dextrose which they can supply, and the chemical equa- 
tions already given on pp. 38 and 51 are claimed to show sub- 
stantially what that amount is. The carbohydrates, according to 
this theory, yield practically their entire store of energy to the 
organism, while if the equations mentioned are interpreted liter- 
ally the sugar produced from one gram of proteids would, accord- 
ing to Chauveau’s equation, contain but about 1.83 Cals. of poten- 
tial energy in place of the 4.4 Cals. available from the proteids 
according to Rubner. If the proteids are assumed to be split 
up in accordance with Gautier’s equation the resulting dextrose 
would contain about 80 per cent. of their potential energy, and 
this figure is used in computing their isoglycosic value. Similarly, 
the sugar derived from one gram of fat would contain about 6.07 
Cals. out of the 9.5 Cals. contained in the original fat. In other 
words, while Chauveau does not question that the actual food of 
the living cells is of value in proportion as it supplies energy, he 
holds that in the complex organism of the higher animals a con- 
siderable share of the original potential energy of fats and proteids 
is lost during their conversion into material (carbohydrates) which 
the cells can use. 
The conception of the mutual replacement of the nutrients on 
the basis of the amounts of energy they are capable of liberating 
for the use of the organism has proved a fruitful one and been the 
basis of much subsequent research. A full discussion of it and 
*La Vie et l’Energie chez l’Animale. 
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