e term metabolism.
The metabolism of matter in the body is governed largely by the needs of
the body for energy. The science of nutrition, of which the present
subject forms a part, is based on the principle that the transformations
of matter and energy in the body occur in accordance with the laws of
the conservation of matter and of energy. That the body can neither
create nor destroy matter has long been universally accepted. It would
seem that the transformation of energy must likewise be governed by the
law of the conservation of energy; indeed there is every reason a priori
to believe that it must; but the experimental difficulties in the way of
absolute demonstration of the principle are considerable. For such
demonstration it is necessary to prove that the income and expenditure
of energy are equal. Apparatus and methods of inquiry devised in recent
years, however, afford means for a comparison of the amounts of both
matter and energy received and expended by the body, and from the
results obtained in a large amount of such research, it seems probable
that the law obtains in the living organism in general.

The first attempt at such demonstration was made by M. Rubner[3] in
1894, experimenting with dogs doing no external muscular work. The
income of energy (as heat) was computed, but the heat eliminated was
measured. In the average of eight experiments continuing forty-five
days, the two quantities agreed within 0.47%, thus demonstrating what it
was desired to prove--that the heat given off by the body came solely
from the oxidation of food within it. Results in accordance with these
were reported by Studenski[4] in 1897, and by Laulanie[5] in 1898.

The most extensive and complete data yet available on the subject have
been obtained by W. O. Atwater, F. G. Benedict and associates[6] in
experiments with men in the respiration calorimeter, in which a subject
may remain for several consecutive days and nights. These experiments
involve actual weighing and analyses of the food and drink, and of the
gaseous, liquid and solid excretory products; determinations of
potential energy (heat of oxidation) of the oxidizable material received
and given off by the body (including estimation of the energy of the
material gained or lost by the body); and measurements of the amounts of
energy expended as heat and as external muscular work. By October 1906
eighty-eight experiments with fifteen different subjects had been
complet