The science of life : fully illustrated in tone and line and including many diagrams

BOOK 1

Thus far the bodies of the mouse and the man are very much alike. Both possess limbs and chests and abdomens, hearts and spinal cords and bowels. But when we come to the lower end of the body we find a serious divergence between human and murine anatomy. A man terminates in a smooth, pink expanse of skin, but a mouse continues into a long and ingeniously movable tail. In a fish the tail is even more important; it is the principal organ of locomotion, and includes all the bones, muscles, blood-vessels and nerves that are necessary for movement in a limb. The tail of a mouse is less important. The mouse propels himself chiefly by means of his limbs, and although the tail is used for balancing the body and for getting a firm grip in climbing, it is by no means his chief organ of propulsion. It includes the same organs as the tail of a fish, but very much more poorly developed. In ourselves the tail is represented by a useless little curling end of the vertebral column that does not even project from the surface of the body. At least this is true of our adult selves; as embryos we had perfectly good tails, as we shall tell later.

So, with apologies, we tell over again what everybody knows, and review the general lay-out of a man. And having made quite sure where our heads and tails are, we will now go on a little more precisely to other matters, also very widely known but not so extensively and not nearly so exactly as what has gone before.

§ 2.

About Cells ; the Lesser Lives within our Life

We have shown in Chapter One that the human body is fundamentally a machine. We have now to explain that it is not a simple machine. It is a great mechanical system made up of an almost infinite multitude of smaller machines.

We remarked in the introduction that one of the most important and revolutionary extensions of the science of life occurred when the microscope came to bear upon living structures. Before that time the wisest men knew no more about the composition of flesh and blood than the most ignorant butcher who ever cut up a carcass. Many philosophers knew less. Now nearly everyone knows that the blood is full of billions of microscopic bodies called blood corpuscles and that most of our bodies are built up of units called ‘cells,’ as a wall is built of bricks or a cotton strand of fibres.

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THE SCIENCE OF LIFE

CHAPTER 2

The word “cell” is a most unfortunate word in this connexion. That is why the triplex writer has put fastidious inverted commas about it in the last two sentences. He dislikes handling and using it. He has to do so, but thus he shows his reluctance. The old original meaning, the proper meaning of “cell,” was a compartment, an enclosure. We still talk of the hermit’s cell or a cell in a prison. And many people at the outset of their biological reading are misled, therefore, into imagining that our livmg tissues have a sort of honeycomb structure. Nothing could be farther from the reality. The proper word should be “ corpuscle”’ (little body) and not cell at all. Only comparatively few of our own cells are imprisoned in a case. Yet the misnomer arose very easily and naturally. Hooke, in 1667, peered down a microscope at a thin slice of dead cork, and found it to consist of an enormous number of tiny empty boxes fitted closely together, and cells seemed to be the only proper word for them. His observation was extended to a considerable number of other vegetable substances, and in all of them he found cells likewise. Very gradually the interest of investigators shifted from the boxes to the contents, but not abruptly enough to rechristen these objects. In living cork, or in the other tissues of a plant, the cell walls are inhabited by pieces of a slimy, gelatinous substance called protoplasm, and it is to these contents, and not to their prisons, that the word cell is now applied. It is the protoplasm and not its garment which makes the cell. In animal tissues we find the cell without the box. The protoplasm may go bare; “ the cell’s the cell, for a’ that.”

Most cells, but not all of them, are microscopic. Some vegetable cells are big enough to see—the cells of elder pith, for example, and any egg before it begins to develop. The yolk of a new-laid hen’s egg is a single cell. But the very great majority of cells are invisibly minute. And they are things with a structure of their own. They are not just lumps of this protoplasm. Their peculiarities

-will be best understood if we describe one

or two different kinds of them.

Take, for example, a shred of body substance of any kind—any “tissue” as the professor loves to call it—a bit of liver, say, or of brain, or of muscle from the stomach—and put it under a microscope, and immediately the division into cells is quite manifest. Figure 9 shows greatly magnified the minute structure of a thin sheet of tissue that lines the cavity of the belly and sheathes