ted, that the source of animal heat is really the consumption
of the fuel taken in through the stomach and the lungs. He showed that
all the activities of life are really the product of energy liberated
solely through destructive processes, amounting, broadly speaking, to
combustion occurring in the ultimate cells of the organism. Here is his
argument:

LIEBIG ON ANIMAL HEAT

"The oxygen taken into the system is taken out again in the same forms,
whether in summer or in winter; hence we expire more carbon in cold
weather, and when the barometer is high, than we do in warm weather; and
we must consume more or less carbon in our food in the same proportion;
in Sweden more than in Sicily; and in our more temperate climate a full
eighth more in winter than in summer.

"Even when we consume equal weights of food in cold and warm countries,
infinite wisdom has so arranged that the articles of food in different
climates are most unequal in the proportion of carbon they contain. The
fruits on which the natives of the South prefer to feed do not in the
fresh state contain more than twelve per cent. of carbon, while the
blubber and train-oil used by the inhabitants of the arctic regions
contain from sixty-six to eighty per cent. of carbon.

"It is no difficult matter, in warm climates, to study moderation in
eating, and men can bear hunger for a long time under the equator; but
cold and hunger united very soon exhaust the body.

"The mutual action between the elements of the food and the oxygen
conveyed by the circulation of the blood to every part of the body is
the source of animal heat.

"All living creatures whose existence depends on the absorption of
oxygen possess within themselves a source of heat independent of
surrounding objects.

"This truth applies to all animals, and extends besides to the
germination of seeds, to the flowering of plants, and to the maturation
of fruits. It is only in those parts of the body to which arterial
blood, and with it the oxygen absorbed in respiration, is conveyed that
heat is produced. Hair, wool, or feathers do not possess an elevated
temperature. This high temperature of the animal body, or, as it may be
called, disengagement of heat, is uniformly and under all circumstances
the result of the combination of combustible substance with oxygen.

"In whatever way carbon may combine with oxygen, the act of combination
cannot take place without the disengagement of heat. It is a m