were still farther from a complete knowledge of phenomena, even those
of fundamental importance.

Liebig asked if we could distinguish, on the one hand, between the
kind of food which goes to create warmth and, on the other, that by
the oxidation of which the motions and mechanical energy of the body
are kept up. He thought he was able to do this, and he divided food
into two categories. The starchy or carbo-hydrate food was that, said
he, which by its combustion provided the warmth necessary for the
existence and life of the body. The albuminous or nitrogenous
constituents of our food, the flesh meat, the gluten, the casein out
of which our muscles are built up, were not available for the purpose
of creating warmth, but it was by the waste of those muscles that the
mechanical energy, the activity, the motions of the animal are
supplied.

Soon after the promulgation of these views, J.R. Mayer warmly attacked
them, throwing out the hypothesis that all muscular action is due to
the combustion of food, and not to the destruction of muscle.

What did modern research say to this question? Could it be brought to
the crucial test of experiment? It could; but how? In the first place,
we could ascertain the work done by a man or any other animal; we
could measure this work in terms of our mechanical standard, in
kilogramme-meters or foot-pounds. We could next determine what was the
destruction of nitrogenous tissue at rest and under exercise by the
amount of nitrogenous material thrown off by the body. And here we
must remember that these tissues were never completely burned, so that
free nitrogen was never eliminated. If now we knew the heat value of
the burned muscle, it was easy to convert this into its mechanical