individuals to continue to exist for
months and years without the ingestion of nutriment into the system, it
is undoubtedly true that under certain circumstances life can be
prolonged for days and weeks without any food of any kind going into the
organism.

The body is a machine constructed for the purpose of working. The kinds
of work which the body of a man or woman does are many. Every act of
perception or sensation, is an act of work; so is every thought, every
emotion, every volition. The action of the heart or lungs in the
circulation and respiration, the evolution of the animal heat, the
various functions of secretion and excretion, digestion, motion,
speech, etc., are all so many kinds of work. Now as regards work, it is
well known that for its due performance force is required, and it is
equally well known that for the development of force, matter that can be
metamorphosed is necessary. The engine may be perfect, the water may be
in the boiler, but unless there be force in the form of heat there will
be no steam; and there will be no heat unless there be fuel in a state
of combustion.

The human body differs from any other machine in the fact that it uses
its fuel in great part indirectly; only in fact after it has been
assimilated and converted into tissues of various kinds. Thus when a
muscle contracts, it is the muscle itself which is consumed; when a
thought is conceived it is the brain which provides the force; when an
emotion is experienced, it is again the brain which is decomposed. The
body, therefore, lives by the death of its own substance. It is true,
some kinds of food such as alcohol, tea and coffee, and perhaps some
others do not require to go farther than the blood to be burned, but
these are mainly heat-producing, and not tissue-producing substances.
But whether matter be consumed directly or indirectly, all bodily force
results from its decomposition, and without this destruction of matter
the body would be absolutely incapable of a single functional action of
any kind whatever, and its temperature like that of the so-called
cold-blooded animals would be that of the surrounding medium, the
atmosphere.

The quantity of food required by the system varies like the demands of
other machines in accordance with the amount of work which is to be
performed. A plowman, other things being equal, consumes more than a
watchmaker; just as a locomotive burns more fuel than the little engine
that runs a s