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 substances.

I shall only add that Professor Yaeger's theory may be carried farther yet. Each metal has also a certain taste and odour peculiar to itself; in other words, they are also endowed with odoriferous substances. And this may help us to explain the fact that each metal, when crystallizing out of a liquid solution, invariably assumes a distinct geometrical form, by which it may be distinguished from any other. Common salt, for instance, invariably crystallizes in cubes, alum in octohedra, and so on.

Professor Yaeger's theory explains further to us that other great mystery of Nature—the transmission from parent to offspring of the morphological speciality. This is another puzzle of the biologist. What is there in the embryonal germ that evolves out of the materials stored up therein a frame similar to the parents? In other words, what is there that presides over the preservation of the species, working out the miniature duplicate of the parents' configuration and character? It is the protoplasm, no doubt; and the female ovum contains protoplasm in abundance. But neither the physicist nor the chemist can detect any difference between the primordial germ, say of the fowl, and that of a female of the human race.

In answer to this question—a question before which science stands perplexed—we need only remember what has been said before about the protoplasmic scent. We have spoken before of the specific scent of the animal as a whole. We know, however, that every organ and tissue in a given animal has again its peculiar scent and taste. The scent and taste of the liver, spleen, brain, &c., are quite different in the same animal.

And if our theory is correct, then it could not be otherwise. Each of these organs is differently constructed, and as variety of organic structure is supposed to be dependent upon variety of scent, there must necessarily be a specific cerebral scent, a specific splenetic scent, a specific hepatic scent, &c. &c. What we call, then, the specific scent of the living animal must, therefore, be considered as the aggregate of all the different scents of its organs.

When we see that a weak solution of sulphuric acid is capable of disengaging from the blood the scent of the animal, we shall then bear in mind that this odorous emanation contains particles of all the scents peculiar to each tissue and organ of the animal. When we further say that each organ in a living animal draws by selective affinity from the blood those materials which are necessary for its sustenance, we must not forget that each organ draws at the same time by a similar selective affinity the specific odorous substances requisite for its constructive requirements.

We have now only to suppose that the embryonal germ contains, like the blood itself, all the odorous substances pertaining to the various tissues and organs of the parent, and we shall understand which is the moving principle in the germ that evolves an offspring, shaped in the image and after the likeness of the parents.