atter of
indifference whether the combination takes place rapidly or slowly, at a
high or at a low temperature; the amount of heat liberated is a constant
quantity. The carbon of the food, which is converted into carbonic acid
within the body, must give out exactly as much heat as if it had been
directly burned in the air or in oxygen gas; the only difference is that
the amount of heat produced is diffused over unequal times. In oxygen
the combustion is more rapid and the heat more intense; in air it is
slower, the temperature is not so high, but it continues longer.

"It is obvious that the amount of heat liberated must increase or
diminish with the amount of oxygen introduced in equal times by
respiration. Those animals which respire frequently, and consequently
consume much oxygen, possess a higher temperature than others which,
with a body of equal size to be heated, take into the system less
oxygen. The temperature of a child (102 degrees) is higher than that of
an adult (99.5 degrees). That of birds (104 to 105.4 degrees) is higher
than that of quadrupeds (98.5 to 100.4 degrees), or than that of fishes
or amphibia, whose proper temperature is from 3.7 to 2.6 degrees higher
than that of the medium in which they live. All animals, strictly
speaking, are warm-blooded; but in those only which possess lungs is the
temperature of the body independent of the surrounding medium.

"The most trustworthy observations prove that in all climates, in the
temperate zones as well as at the equator or the poles, the temperature
of the body in man, and of what are commonly called warm-blooded
animals, is invariably the same; yet how different are the circumstances
in which they live.

"The animal body is a heated mass, which bears the same relation to
surrounding objects as any other heated mass. It receives heat when the
surrounding objects are hotter, it loses heat when they are colder
than itself. We know that the rapidity of cooling increases with
the difference between the heated body and that of the surrounding
medium--that is, the colder the surrounding medium the shorter the time
required for the cooling of the heated body. How unequal, then, must be
the loss of heat of a man at Palermo, where the actual temperature is
nearly equal to that of the body, and in the polar regions, where the
external temperature is from 70 to 90 degrees lower.

"Yet notwithstanding this extremely unequal loss of heat, experience
has shown t