The Organic World

Under favoring conditions, protoplasm has a power of performing chemical changes, which result in producing heat far more gently and continuously than it is produced by the combustion of inorganic bodies. Thus it is that the heat is produced which makes its presence evident to us in what we call "warm-blooded animals," the most warm-blooded of all being birds.

Protoplasm has also the wonderful power of transforming certain adjacent substances into material like itself—into its own substance—and so, in a sense, creating a new material. Thus it is that organisms have the power to nourish themselves and grow. An animal would vainly swallow the most nourishing food if the ultimate, protoplasmic particles of its body had not this power of "transforming" suitable [pg 362] substances brought near them in ways to be hereinafter noticed.

Without that, no organism could ever "grow." The growth of organisms is utterly different from the increase in size of inorganic bodies. Crystals, as we have seen, grow merely by external increment; but organisms grow by an increment which takes place in the very innermost substance of the tissues which compose their bodies, and the innermost substance of the cells which compose such tissues; this peculiar form of growth is termed intussusception.

Protoplasm, after thus augmenting its mass, has a further power of spontaneous division, whereby the mass of the entire organism whereof such protoplasm forms a part, is augmented and so growth is brought about.

The small particles of protoplasm which constitute "cells" are far indeed from being structureless. Besides the nucleus already mentioned there is a delicate network of threads of a substance called chromatin within it, and another network permeating the fluid of the cell substance, which invest the nucleus often with further complications. These networks generally perform (or undergo) a most complex series of changes every time a cell spontaneously divides. In certain cases, however, it appears that the nucleus divides into two in a more simple fashion, the rest of the cell contents subsequently dividing—each half enclosing one part of the previously divided nucleus. It is by a continued process of cell division that the complex structures of the most complex organisms is brought about.

The division of a cell, or particle of protoplasm, is [pg 363] indeed a necessary consequence of its complete nutrition.

For new material can only be absorbed by its surface. But as the cell grows, the proportion borne by its surface to its mass, continually decreases; therefore this surface must soon be too small to take in nourishment enough, and the particle, or cell, must therefore either die or divide. By dividing, its parts can continue the nutritive process till their surface, in turn, becomes insufficient, when they must divide again, and so on. Thus the term "feeding" has two senses. "To feed a horse," ordinarily means to give it a certain quantity of hay, oats or what not; and such indeed is one kind of feeding. But obviously, if the nourishment so taken could not get from the stomach and intestines into the ultimate particles and cells of the horse's body, the horse could not be nourished, and still less could it grow. It is this latter process, called assimilation, which is the real and essential process of feeding, to which the process ordinarily so called is but introductory.

Protoplasm has also the power of forming and ejecting from its own substance, other substances which it has made, but which are of a different nature to its own. This function, as before said, is termed secretion; and we know the liver secretes bile, and that the cow's udder secretes milk.

Here again we have an external and an internal process. The milk is drawn forth from a receptacle, the udder, into which it finds its way, and so, in a superficial sense, it may be called an organ of secretion. Nevertheless the true internal secretion takes place in [pg 364] the innermost substance of the cells or particles of protoplasm, of the milk-land, which particles really form that liquid.

FIG. 4. AMOEBA SHOWN IN TWO OF THE MANY IRREGULAR SHAPES IT ASSUMES. (After Howes.)

The clear space within it is a contractile vesicle. The dark body is the nucleus. In the right-hand figure there is shown a particle of food, passing through the external surface.

But every living creature consists at first entirely of a particle of protoplasm. Therefore every other kind of substance which may be found in every kind of plant or animal, must have been formed through it, and be, in fact, a secretion from protoplasm. Such is the rosy cheek of an apple, or of a maiden, the luscious juice of the peach, the produce of the castor-oil plant, the baleen that lines the whale's enormous jaws, as well as that softest product, the fur of the chinchilla. Indeed, every particle of protoplasm requires, in order that it may live, a continuous process of exchange. It needs to be continuously first built up by food, and then broken down by discharging what is no longer needful for its healthy existence. Thus the life of every organism is a life of almost incessant change, not only in its being as a whole, but in that of all its protoplasmic particles also.

Prominent among such processes is that of an interchange of gases between the living being and its environment. This process consists in an absorption of oxygen and a giving-out of carbonic acid, which exchange is termed respiration.

Lastly, protoplasm has a power of motion when appropriately acted on. It will then contract or expand its shape by alternate protrusions and retractions of parts of its substance. These movements are termed amoebiform, because they quite resemble the movements of a small animalcule which is named amoeba. (See Fig. 4.)

Such is the ultimate structure, and such are the fundamental activities or functions of living organisms, as far as they can here be described, from the lowest animalcule and unicellular plant, up to the most complex organisms and the body of man himself.

Contents