786 The American Naturalist. [October, 
ence to our present subject, the following table, showing the 
percentage of food constituents found in the increase of fatten- 
ing animals at Rothamsted, will serve as a sufficient illustra- 
tion, 
TABLE 1. 
Percentage of food constituents in the increase of fattening animals. 
Stored in Increase. 
Constituents of Food. ; 
Oxen. Sheep. Pigs. 
Per cent. Per cent. Per cent. 
Proteids 4.1 4.2 13.5 
Carbo-hydrates and fat 7.2 9.4 18.5 
s. E9 St Tid 
Dry Substance 6.2 8.0 17.6 
It will be seen that much the larger part of the food constit- 
uents were not utilized by the animals as materials for build- 
ing tissues, but they have served a useful purpose in 
yielding up more or less of their stored energy, according to 
the degree of disintegration to which they were subjected, 
which was made available in the constructive processes of nu- 
trition and the related incidental physiological activities of the 
system. : 
With this limited demand for the constituents of foods to 
serve as materials for tissue building, there must be an exten- 
sive disintegration of their organic substance to furnish the 
enormous supplies of energy required in the repair of tissues, 
in increase in growth, in the vaporization of water exhaled by 
the lungs and skin, and to supply the sensible residue that is 
lost by constant radiation from the body in the form of ani- 
mal heat. 
The obsolete theory of Liebig that certain food constituents 
are alone used to build tissues and that certain other constitu- 
ents are burned in the system to produce heat, still continues 
to be the leading assumption in attempts to popularize chemi- 
cal theories of nutrition in formulating diets and nutritive 
