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
apparatus.

The obstacles in the way of these experiments do not particularly
concern us, but the general results are of the greatest significance for
our purpose. While, for manifest reasons, it has not been possible to
carry on these experiments for any great length of time, and while the
results have not yet been very accurately refined, they are all of one
kind and teach unhesitatingly one conclusion. So far as concerns
measurable energy or measurable material, the body behaves just like any
other machine. If the body is to do work in this respiration apparatus,
it does so only by breaking to pieces a certain amount of food and using