e 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
feet in length, in which their only communication with the outer world
is by telephone and through a small opening in the side of the chamber,
occasionally opened for a second or two to supply the prisoner with
food. In such a chamber they have remained as long as twelve days. In
these experiments it is necessary to take account not only of the food
eaten, but of the actual amount of this food which is used by the body.
If the person gains in weight, this must mean that he is storing up in
his body material for future use; while if he loses in weight, this
means that he is consuming his own tissues for fuel. Careful daily
records of his weight must therefore be taken. Estimates of the solids,
liquids, and gases given off from his body must be obtained, for to
carry out the experiment an exact balance must be made between the
income and the outgo. The apparatus devised for such experiments has
been made very delicate; so delicate, indeed, that the rising of the
individual in the box from his chair is immediately seen in a rise in
temperature of the apparatus. But even with this delicacy the apparatus
is comparatively coarse, and can measure only the most apparent forms of
energy. The more subtle types of energy, such as nervous force, if this
is to be regarded as energy, do not make any impression on the
app