CHAPTER VI.
POLARITY IN LIFE.
Contrast of living and dead—Eating and being eaten—Trace matter upwards and life downwards—Colloids—Cells—Protoplasm—Monera—Composition of protoplasm—Essential qualities of life—Nutrition and sensation—Motion—Reproduction—Spontaneous generation—Organic compounds—Polar conditions of life.
Polarity having been established as the universal law of the inorganic world, we have now to pass to the organic, or world of life. At first sight there seems to be a great gulf fixed between the living and the dead which no bridge can span. But first impressions are very apt to deceive us, and when things are traced up to their origins we often find them getting nearer and nearer until it is difficult to say where one begins and the other ends. Take for instance such an antithesis as ‘eating or being eaten.’ If a hunter meets a grizzly bear in the Rocky Mountains, one would say that no distinction can be sharper than whether the bear eats the man, or the man the bear. In the one case there is a man, and in the other a bear, less in the world. But look through a microscope at a glass of water, and you may see two specks of jelly-like substance swimming in it. They are living creatures, for they eat and grow, and thrust out and retract processes of their formless mass, which serve as temporary legs and arms for seizing food and for voluntary motion. In short, they are each what may be called strictly individual amœbæ, forming separate units of the animated creation as much as the man and the bear. But if the two happen to come in contact, what happens? The two slimy masses involve one another and coalesce, and the resulting amœba swims away merrily as two gentlemen rolled into one.
Now in his case what became of their individualities: did amœba A eat amœba B, or vice versâ, and is the resulting amœba a survival of A or of B, or of both or neither of them? And what becomes of the antithesis of ‘eating or being eaten’ which was so clear and distinct in the highly specialised forms of life, and is so evanescent in the simpler forms? This illustration may serve to teach us how necessary it is to trace things up to their origins, before expressing too trenchant and confident opinions as to their nature and relations.
In the case of the organic and inorganic worlds the proper course obviously is, not to draw conclusions from extreme and highly specialised instances, but to follow life downwards to its simplest and most primitive form, and matter upwards to the form which approaches most nearly to this form of life. Following matter upwards, we find a regular progression from the simple to the complex. Take the diamond, which is one of the simplest of substances, being merely the crystallised form of a single ultimate element, carbon. It is extremely hard and extremely stable. Ascending to compounds of two, three, or more elements, we get substances which are more complex and less stable; and at last we arrive at combinations which involve many elements and are extremely complex. Among these latter substances are some, called colloids, which are neither solid, like crystals, nor fluid, like liquids, but in an intermediate state, like jelly or the white of an egg, in which the molecules have great mobility and are at a considerable distance apart, so that water can penetrate their mass. These colloids are for the most part very complicated compounds of various elements based on a nucleus of carbon, which, from its atom having four poles with strong mutual attractions, is eminently qualified for forming what may be called the inner skeleton of these complex combinations. Colloids of this description form the last stage of the ascending line from inorganic matter to organic life.
Next let us trace life downwards towards matter. There is a constant succession from the more to the less complex and differentiated: from man, through mammals, reptiles, fishes, and a long chain of more simple forms, until at its end we come to the two last links, which are the same for all animals, all plants, and all forms of animated existence. The last link but one is the cell, the last of all is protoplasm.
Protoplasm, or, as Huxley calls it, ‘the physical basis of life,’ is a colourless jelly-like substance, absolutely homogeneous, without parts or structure, in fact a mere microscopic speck of jelly.
The cell is the first step in the specialisation of protoplasm, the outer layer of which, in contact with the surrounding environment, becoming hardened so as to form an enclosing cell-wall, while a portion of the enclosed protoplasm condenses into a nucleus, in which a further condensation makes what is called the nucleolus or second smaller nucleus. This constitutes the nucleated cell, whose repeated subdivision into other similar cells in geometrical progression furnishes the raw material out of which all the varied structures of the world of life are built up. Plants and animals, bones, muscles, and organs of sense, are all composed of modified cells, hardened, flattened, or otherwise altered, as the case may require. If we trace life up to its origin in the individual instead of in the species, we arrive at the same result. All plants and animals, whether of the lowest or highest forms, fish, reptile, bird, mammal, man, begin their individual existence as a speck of protoplasm, passing into a nucleated cell, which contains in it the whole principle of its subsequent evolution into the mature and completed form.