tigations into the immediate products of animal
life. He was the first to demonstrate that the only source of
animal heat is that produced by the oxidation of the tissues.

_I.--Chemical Needs of Life_

Animals, unlike plants, require highly organised atoms for nutriment;
they can subsist only upon parts of an organism. All parts of the animal
body are produced from the fluid circulating within its organism. A
destruction of the animal body is constantly proceeding, every motion is
the result of a transformation of its structure; every thought, every
sensation is accompanied by a change in the composition of the substance
of the brain. Food is applied either in the increase of the mass of a
structure (nutrition) or in the replacement of a structure wasted
(reproduction).

Equally important is the continual absorption of oxygen from the
atmosphere. All vital activity results from the mutual action of the
oxygen of the atmosphere and the elements of food. According to
Lavoisier, an adult man takes into his system every year 827 lb. of
oxygen, and yet he does not increase in weight. What, then, becomes of
this oxygen?--for no part of it is again expired as oxygen. The carbon
and hydrogen of certain parts of the body have entered into combination
with the oxygen introduced through the lungs and through the skin, and
have been given out in the form of carbonic acid and the vapour of
water.

Now, an adult inspires 32-1/2 oz. of oxygen daily; this will convert the
carbon of 24 lb. of blood (80 per cent. water) into carbonic acid. He
must, therefore, take as much nutriment as will supply the daily loss.
And, in fact, it is found that he does so; for the average amount of
carbon in the daily food of an adult man is 14 oz., which requires 37
oz. of oxygen for its conversion into carbonic acid. The amount of food
necessary for the support of the animal body must be in direct ratio to
the quantity of oxygen taken into the system. A bird deprived of food
dies on the third day; while a serpent, which inspires a mere trace of
oxygen, can live without food for three months. The number of
respirations is less in a state of rest than in exercise, and the amount
of food necessary in both conditions must vary also.

The capacity of the chest being a constant quantity, we inspire the same
volume of air whether at the pole or at the equator; but the weight of
air, and consequently of oxygen, varies with the temperature. Thus