and sodium, two more of the elements of animal structures,
produce, in combination, common salt,--without which our food would be
so insipid, that we have the best evidence of its being a necessary
article of diet. The body has many uses for salt. It is found in the
tears, as we are informed by poets, who talk of "briny drops" and "saut,
saut tears"; though why there, unless to keep the lachrymal fluid from
spoiling, in those persons who bottle up their tears for a long time, we
cannot divine.

Perhaps we had better take the rest into consideration together,--the
magnesia and iron, and whatever other elements are found in the body.
Though some of them are there in minute quantities, the structure cannot
exist without them,--and for their constant and sufficient supply our
food must provide.

To see what becomes of all these materials after we have done with them,
we must extend our inquiries among the articles of ordinary diet and
ascertain from what sources we derive the several elements.

It has been sometimes believed that none but animal food contains all
the elements required for the support of life. Thanks to Liebig, we have
discovered that vegetable substances also, fruits, grains, and
roots, contain them all, and, in most cases, in very nearly the same
proportions as they are found in animals. We are not lecturing on
dietetics; therefore we will not pause to explain why, although either
bread or meat alone contains the various materials for flesh and bone,
it is better to combine them than to endeavor to subsist on one only.

Whither, then, go these elements when man has done with them? The answer
is,--All Nature wants them. Every plant is ready to drink them up, as
soon as they have taken forms which bring them within its reach. As
gases, they are inhaled by the leaves, or, dissolved in water, they
are drunk up by the roots. All plants have not the same appetites, and
therefore they can make an amicable division of the supply. Grasses and
grains want a large proportion of phosphate of lime, which they convert
into husks. Peas and beans have little use for nitrogen, and resign it
to others. Cabbages, cauliflowers, turnips, and celery appropriate a
large share of the sulphur.

The food of plants and that of animals have this great difference:
plants take their nourishment in inorganic form only; animals require
to have their food in organic form. That is, all the various
minerals, singly or combined, which c