upposed that one of
the causes of consumption is the deficiency of phosphate of lime in
food.

[Why is the heat produced by combustion apparent?

Explain the production of heat in the lungs of animals?

Why does exercise augment the animal heat?

Under what circumstances is the animal's own fat used in the production
of heat?]

The first class of proximates (starch, sugar, gum, etc.), perform an
important office in the animal economy aside from their use in making fat.
They constitute the _fuel_ which supplies the animal's fire, and gives him
his _heat_. The lungs of men and other animals may be called delicate
_stoves_, which supply the whole body with heat. But let us explain this
matter more fully. If wood, starch, gum, or sugar, be burned in a stove,
they produce heat. These substances consist, as will be recollected, of
carbon, hydrogen, and oxygen, and when they are destroyed in any way
(provided they be exposed to the atmosphere), the hydrogen and oxygen unite
and form water, and the carbon unites with the oxygen of the air and forms
carbonic acid, as was explained in a preceding chapter. This process is
always accompanied by the liberation of _heat_, and the _intensity_ of this
heat depends on the _time_ occupied in its _production_. In the case of
decay, the chemical changes take place so slowly that the heat, being
conducted away as soon as formed, is not perceptible to our senses. In
combustion (or burning) the same changes take place with much greater
rapidity, and the same _amount_ of heat being concentrated, or brought out
in a far shorter time, it becomes intense, and therefore apparent. In the
lungs of animals the same law holds true. The blood contains matters
belonging to this carbonaceous class, and they undergo in the lungs the
changes which have been described under the head of combustion and decay.
Their hydrogen and oxygen unite, and form the moisture of the breath, while
their carbon is combined with the oxygen of the air drawn into the lungs,
and is thrown out as carbonic acid. The same consequence--heat--results in
this, as in the other cases, and this heat is produced with sufficient
rapidity for the animal necessities. When an animal exercises violently,
his blood circulates with increased rapidity, thus carrying carbon more
rapidly to the lungs. The breath also becomes quicker, thus supplying
increased quantities of oxygen. In this way the decomposition becomes more
rapid, and the anima