evident that it demands no further demonstration. The details of the
problem may, however, present some difficulties.

The first question which presents itself is whether the only power the
body possesses is, as in the case with other machines, to _transform_
energy without being able to create or destroy it? Can every bit of
energy shown by the living organism be accounted for by energy furnished
in the food, and conversely can all the energy furnished in the food be
found manifested in the living organism?

The theoretical answer to this question in terms of the law of the
conservation of energy is clear enough, but it is by no means so easy to
answer it by experimental data. To obtain experimental demonstration it
would be necessary to make an accurate determination of the amount of
energy an individual receives during a given period, and at the same
time a similar measurement of the amount of energy liberated in his body
either as motion or heat. If the body is a machine, these two should
exactly balance, and if they do not balance it would indicate that the
living organism either creates or destroys energy, and is therefore not
a machine. Such experiments are exceedingly difficult. They must be
performed usually upon man rather than other animals, and it is
necessary to inclose an individual in an absolutely sealed space with
arrangements for furnishing him with air and food in measured quantity,
and with appliances for measuring accurately the work he does and the
heat given off from his body. In addition, it is necessary to measure
the exact amount of material he eliminates in the form of carbonic acid
and other excretions. Such experiments present many difficulties which
have not yet been thoroughly overcome, but they have been attempted by
several investigators. For the purpose of such an experiment scientists
have allowed themselves to be shut up in a small chamber six or eight