Page:Popular Science Monthly Volume 45.djvu/541

Rh point, and the viscous drop, changing shape continually, seems to flow along slowly. If it meets any vegetable matter, it envelops it, and the stuff suffers a real digestion. The residue is cast out, as it was absorbed, by any point of the surface. We call these beings amœbas. They are capable of multiplication by division, and every part of them is susceptible of being indifferently surface or inside, the drawing part or the part drawn, mobile all at once. For the amœba can choose its direction and find more light or more darkness according to what we may call its aspirations, since it acts, definitively, as a living being.

If we open a tan vat in the spring, we shall discover here and there irregular golden-yellow filaments, soft and slimy. We observe them changing their place and flowing like the amœbas. They appear to be seeking one another in the mass of tan, for in the summer, after a shower, they may be seen to join, then rise in the shape of a kind of yellow cake, large and thick as the two hands; the botanists call them myxomyceta, or the slimy fungus. Detach a part of this mass, put it on a potsherd, and it will, like the amœba, extend branchy expansions, pass itself upon them, stretch out and return upon itself in changing lumps, to be succeeded soon by new stretchings.

We see in these, beings without form, without organs, composed solely of an opaque substance, and highly colored in the myxomycetes, but transparent in the amœba, a little denser than water, with which it does not mix, a substance that moves and feels—that is, that shares with us the higher attributes of life. The discovery of the amœbas was at first merely a curiosity till Dujardin and Hugo Mohl, almost at the same time, called attention to a substance entering into the composition of infusoria and the cells of plants that had all the characteristics of the substance of the amœbas. Dujardin called it sarcode; Hugo Mohl, protoplasma, and that name prevailed. The term, imposed as the name of one of the constituent parts of the vegetable cell, has had the singular fortune to become almost synonymous with matter living or that has lived.

This amorphous substance is the basis of the organism. In plants, it is what in some way builds up every cell, as the worm and the mollusk produce the shell and the tube that protect them, or as the caterpillar envelops itself with the cocoon which it draws out from its glands. So the protoplasm molds around itself the walls of the cell in which it is inclosed. But it is always the prime living part, and when it disappears the cellular wall becomes only an inert body. In animals, likewise, the egg, or at least its essential part, the vitellus, shows in its almost universal spherical form the protoplasm shaped at first only by the laws of attraction and resistance common to all matter. But when the egg takes life, the