g in plants are either rejected by animals or else
they occur in the food in such very small proportion that they cannot
possibly contribute to the increase of mass in the animal body.

The chemical analysis of these three substances has led to the
interesting result that they contain the same organic elements, united
in the same proportion by weight; and--which is more remarkable--that
they are identical in composition with the chief constituents of
blood--animal fibrine and animal albumen. By identity, be it remarked,
is not here meant merely similarity, but that even in regard to the
presence and relative amounts of sulphur, phosphorus, and phosphate of
lime no difference can be observed.

How beautifully simple then, by the aid of these discoveries, appears
the process of nutrition in animals, the formation of their organs, in
which vitality chiefly resides. Those vegetable constituents which are
used by animals to form blood contain the essential ingredients of blood
ready formed. In point of fact, vegetables produce in their organism the
blood of all animals; for the carnivora, in consuming the blood and
flesh of the graminivora, consume, strictly speaking, the vegetable
principles which have served for the nourishment of the latter. In this
sense we may say the animal organism gives to blood only its form; and,
further, that it is incapable of forming blood out of other compounds
which do not contain the chief ingredients of that fluid.

Animal and vegetable life are, therefore, closely related, for the first
substance capable of affording nutriment to animals is the last product
of the creative energy of vegetables. The seemingly miraculous in the
nutritive power of vegetables disappears in a great degree, for the
production of the constituents of blood cannot appear more surprising
than the occurrence of the principal ingredient of butter in palm-oil
and of horse-fat and train-oil in certain of the oily seeds.

_IV.--Food the Fuel of Life_

We have still to account for the use in food of substances which are
destitute of nitrogen but are known to be necessary to animal life. Such
substances are starch, sugar, gum, and pectine. In all of these we find
a great excess of carbon, with oxygen and hydrogen in the same
proportion as water. They therefore add an excess of carbon to the
nitrogenised constituents of food, and they cannot possibly be employed
in the production of blood, because the nitrogenised comp