hrough the scale of retrograde metamorphosis; and it is they that
give rise to what we have called the smell of the animal. What lives in
them is the protoplasm.

In the shape of food the outer world supplies the organism with all the
materials necessary for the building up of the constantly wasting
organic structures; and, in the shape of heat, there comes from the
outer world that other element necessary for structural changes,
development and growth--the element of force. But the task of directing
all the outward materials to the development and maintenance of the
organism--in other words, the task of the director-general of the
organic economy falls to the protoplasm.

Now this wonderful substance, chemically and physically the same in the
highest animal and in the lowest plant, has been all along the puzzle of
the biologist. How is it that in man protoplasm works out human
structure; in fowl, fowl structure, &c. &c., while the protoplasm
itself appears to be everywhere the same? To Professor Yaeger belongs
the great merit of having shown us that the protoplasms of the various
species of plants and animals are not the same; that each of them
contains, moreover, imbedded in its molecules, odorant substances
peculiar to the one species and not to the other.

That, on the other hand, those odorous substances are by no means
inactive bodies, may be inferred from their great volatility, known as
it is in physical science that volatility is owing to a state of atomic
activity. Prevost has described two phenomena that are presented by
odorous substances. One is that, when placed on water, they begin to
move; and the other is, that a thin layer of water, extended on a
perfectly clean glass plate, retracts when such an odorous substance as
camphor is placed upon it. Monsieur Ligeois has further shown that the
particles of an odorous body, placed on water, undergo a rapid division,
and that the movements of camphor, or of benzoic acid, are inhibited, or
altogether arrested, if an odorous substance be brought into contact
with the water in which they are moving.

Seeing, then, that odorous substances, when coming in contact with
liquid bodies, assume a peculiar motion, and impart at the same time
motion to the liquid body, we may fairly conclude that the specific
formative capacity of the protoplasm is owing, not to the protoplasm
itself, since it is everywhere alike, but to the inherent, specific,
odoriferous su