my
honored predecessor in this chair, bought a country-place, including half
of an old orchard. A few years afterwards I saw the trees on his side of
the fence looking in good health, while those on the other side were
scraggy and miserable. How do you suppose this change was brought about?
By watering them with Fowler's solution? By digging in calomel freely
about their roots? Not at all; but by loosening the soil round them, and
supplying them with the right kind of food in fitting quantities.

Now a man is not a plant, or, at least, he is a very curious one, for he
carries his soil in his stomach, which is a kind--of portable flower-pot,
and he grows round it, instead of out of it. He has, besides, a
singularly complex nutritive apparatus and a nervous system. But
recollect the doctrine already enunciated in the language of Virchow,
that an animal, like a tree, is a sum of vital unities, of which the cell
is the ultimate element. Every healthy cell, whether in a vegetable or
an animal, necessarily performs its function properly so long as it is
supplied with its proper materials and stimuli. A cell may, it is true,
be congenitally defective, in which case disease is, so to speak, its
normal state. But if originally sound and subsequently diseased, there
has certainly been some excess, deficiency, or wrong quality in the
materials or stimuli applied to it. You remove this injurious influence
and substitute a normal one; remove the baked coal-ashes, for instance,
from the roots of a tree, and replace them with loam; take away the salt
meat from the patient's table, and replace it with fresh meat and
vegetables, and the cells of the tree or the man return to their duty.

I do not know that we ever apply to a plant any element which is not a
natural constituent of the vegetable structure, except perhaps
externally, for the accidental purpose of killing parasites. The whole
art of cultivation consists in learning the proper food and conditions of
plants, and supplying them. We give them water, earths, salts of various
kinds such as they are made of, with a chance to help themselves to air
and light. The farmer would be laughed at who undertook to manure his
fields or his trees with a salt of lead or of arsenic. These elements
are not constituents of healthy plants. The gardener uses the waste of
the arsenic furnaces to kill the weeds in his walks.

If the law of the animal cell, and of the animal organism, which is built