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

BOOK 1

capillaries, and perspiration. The skin is an adjustable radiator. By dilating the blood-vessels in the skin the amount of blood that is exposed to the cooling action of the air can be increased: therefore we redden when we are too hot. We are increasing the amount of blood in our aircoated radiator. Conversely when we are too cold the vessels of our skins contract ; we blench and the skin pales, and may even become bluish from lack of bright red oxygenated blood. Perspiration is due to the action of the sweat-glands, which pour out on to the surface of the skin a fluid that consists very largely of water. That evaporates and cools us. It is our most effective method of temperature regulation. By sweating and so cooling his body a man can stand exposure to a temperature at which water. would boil. As early as 1775, a Mr. Blagden reported to the Royal Society experiments on this subject. He describes how he and others who stayed for some time in a dry-heated room at the temperature of boiling water found that “ the air heated to these degrees felt unpleasantly hot, but was very bearable.” They were particularly struck by their power of keeping their own temperature constant in spite of the heat around. ‘‘ Whenever we breathed on the thermometer, the quick-silver sank several degrees. Every expiration gave a very pleasant impression of coolness to our nostrils.”

It is indeed perfectly possible for a living man to remain in a hot chamber long enough to see the dead flesh of a mutton chop cooked by the same heat that his temperature-regulating machinery enables him to withstand.

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THE SCIENCE OF LIFE

CHAPTER 2

But to endure such heat the air around a man must be dry. If the air is already charged with water-vapour, or if he is immersed in water, his sweat cannot evaporate and is therefore useless; under the circumstances such a temperature would be rapidly fatal. That is why damp heat is so much more oppressive than dry heat.

And so we realize why it is that Mr. Everyman, as he grows older and wiser, and as his heat-regulating devices lose a little of their elasticity, becomes more and more solicitous about his overcoat, his umbrella, his neck wrap, the soundness of his shoes, and the texture of his underclothing. Next perhaps to his urgent need of air and food is protection from these bacteria which pursue him night and day, and from the chill which enfeebles his resistance to them. These invisible enemies may drive him an exile to warmer and drier climates. They may become the dominant interest in his life. So long as he lives he is never safe from them.

We may doubt whether the mouse organization is any better defended than the man organization against infections and chills. If it is troubled less by intelligent anxiety it is probably much more distressed and driven by hunger and fear. But when illness and weakness come upon a mouse it is far more promptly removed from the world, and we do not hear of its distress as we hear of those of the man-machine. It is because Mr. Everyman struggles so persistently against the forces that would destroy him that we are so acutely aware of them in his case.