562 The American Naturalist. [July, 
energy expended directly and indirectly in Nature’s invisible 
unobtrusive work of growing an acre of corn, must. be equiva- 
Ient to the work of 76 horses, day and night, for six months. 
This energy is all derived from the heat and light of 
the sun. The importance of proper soil conditions to favor 
the required transformations of energy in the growth of the 
erop will readily be seen. 
The motive power of the animal machine, in all of its pro- 
cesses of nutrition and growth, is derived exclusively from the 
stored or potential energy of their food, and we may ask how 
this energy is liberated and made available in the animal 
economy. 
As the energy used in its construction is stored up by the 
plant as an essential condition of its constitution, any disin- 
tegration of its organie substance will liberate the stored 
energy in the form of heat. This may be brought about in 
several ways. 1.—The plant may be burned, and the heat 
produeed represents its stored energy. 2.—Microbes feeding 
on organic substances tear them apart and liberate the stored 
energy in the form of heat. The heat produced in the famil- 
iar processes of fermentation and putrefaction, all of which 
are caused by microbes, is but the stored energy of the organic 
substances on which they feed. 3.—The digestive processes 
of animals involve a disintegration of the food constituents, 
and liberate their potential energy for use in the processes of 
animal nutrition. 
Turning now to the table, for the composition of the fat ox, 
we find it represented in division A, as consisting of simple 
elements, and in division B the complex compounds built up 
from these elements are given. It will be seen that work has 
been done, and energy expended in transforming the simple 
elements of division A into the complex compounds of divi- 
sion B, and, as in the case of the corn, the estimated amount 
of this expenditure of energy is given in foot-tons, and horse 
power, in division C of the table. 
The popular notion that the proteids, fat and carbhydrates 
of the corn are directly converted into the proteids and fat of 
the ox that eats them, (division B), does not take into account 
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Mace E T. z ^ 
NR TN LAS PEREAT RAN TRUE ete RMR Be E a 
