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

BOOK 1

upon the bacteria and, incidentally, upon any injured or dying tissue-cells, and consume them ; they take them into their own bodies and digest them. If the injury be a slight _one, and the invading bacteria few and relatively harmless, the leucocytes have no difficulty in cleaning up the situation. A few hours after their entry into the battlearea they have withdrawn, presumably along the lymphatic vessels, and nothing is left but healthy tissue-cells, actively dividing in order to reconstruct the tissue that has been broken down. But if the invasion is more serious the struggle lasts longer. More and more leucocytes are brought to the battle-area, which becomes to the mind

Muscle

Sweat Gland

Oil Gland

Fig. 35. A thin section of the human scalp, magnified, to show how the “‘ roots”? of our hairs are constructed.

of Mr. Everyman “sore and inflamed.” The bacteria, keeping and extending their footing, multiply in the tissues and destroy tissue cells; the leucocytes frantically consume both bacteria and débris, and in excess of zeal, perish themselves of indigestion. At the end of a day or two, if we examine the battlefield with a microscope, we find a mass of dead and dying bacteria and cells, a mass that is disintegrating into the yellowish fluid called ‘‘ matter,’ or pus, and round this mass we find a cordon of living leucocytes, sheathing it and hemming it in so that there can be no further spread of the trouble. Finally, since the bloodsupply of the skin lying over the abscess is

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THE SCIENCE OF LIFE

Hair

GUEGATR AE Rao =

now quite cut off, the skin breaks down and the abscess “ points,” discharging its contents into the outer world. Mr. Everyman washes it, ties it up, and does his best to forget it.

But not always do the leucocytes prevail. And then the bacteria may succeed in invading the blood-stream, and once they have got access to blood-vessels they are swept round the body, and all the tender tissues of Mr. Everyman are at their mercy. This is when the warfare becomes really serious for him. Leucocytes join issue with the bacteria in the blood, fresh armies of leucocytes are formed in the bone-marrow, the lymph glands, and other special centres of proliferation, and at the same time there is a chemical battle between toxins (poisons) and antitoxins. The whole body becomes the seat of war, and the mental serenity of Mr. Everyman has to be subordinated to the urgent struggle. He has a fever, he says, goes to bed in order that his bodily energies may all be mobilized for this war, and he calls in the aid of a doctor, an allied cellcommunity, so to speak, for advice, comfort, and medical munitions for the struggle.

The power to swallow up and destroy hostile cells is not confined to these phagocytes, which wander about in blood and tissue. In the spleen there are localized cells which take in any undesirable bodies from the blood that circulates past them. During undulant fever, for example, the spleen-cells are found to be full of the organisms responsible for that complaint. The two paris of our interior surfaces which are most exposed to infection are also protected in this way, for cells in the liver exercise a similar filtering power on blood from the intestine, and so do cells in the lungs. Moreover, the walls of our intestines are dotted with special oval areas where leucocytes can be formed when necessary. ‘These guard-houses are called Peyer’s patches. Presumably this is because of the bacteria that swarm in our digestive tubes, warmed by our own heat, and taking our food not only out of our mouths but out of ‘our very bowels. To an organism able to resist our digestive juices—and there are many such—the tender intestinal wall affords an easier way of entry into our blood than the horny skin, and it is therefore necessary to garrison strongly that weak point in our defences. The tonsils of the