ny
vegetable products. Hence, that article of food which contains all
these elements in a proper proportion will tend much more to the
growth and strength of the body than those kinds which are deficient
in one or more of them. Much experience on this point, and scientific
research, seem to show that a reasonable amount of animal food in
health tends to give greater strength of muscle, and a more general
sense of fulness, than in ordinary cases a vegetable diet is able to
do, owing to the presence of nitrogen in animal tissues. Yet there are
examples of the healthiest and strongest men, who live years without a
morsel of animal food; and the fact can only be accounted for, by
supposing that the system has the power to make the most economical
use of the little nitrogen offered to it in the food; or else that it
has by some means the power to abstract it from the atmosphere, and
transform it to the living animal substance.

H.

The proximate principles, which are the most important in nourishing
the body, are albumen and fibrin. These constitute the greater part of
all the softer animal tissues, and are also found in certain classes
of vegetables, such as peas, beans, lentils, and many seeds. Hence, in
many cases, a vegetable diet, especially if embracing any of those
articles, would be sufficient to sustain life, even if no animal food
should be eaten. But no animal can exist for a long time if permitted
only to eat substances destitute of nitrogen, as in the case of a dog
fed entirely on sugar, which lived but thirty days. And owing to this
fact, Baron Liebig proposes to call substances used for food,
containing nitrogen, "elements of nutrition," and those containing an
excess of carbon, "elements of respiration;" since, according to his
view, the food is necessary to support the growth of the body by
replacing the effete and worn-out particles with new matter, and also
to keep up the supply of fuel, in order to promote a sufficient degree
of heat in the system. Accordingly, under the first division would be
included all lean meats and vegetables, such as peas, &c.; while the
fat of animals, vegetable oils, sugars, tubers, (as the potato,) and
all other substances containing starch, would be included under the
latter division.

I.

This definition of exhalants is from the theory of Haller and others.
It is now believed that the fluids exude through the thin coats of the
blood vessels. This process is called _