We have already learned that the skin, besides being a covering or protection for the body, is at the same time a special organ with special work to do. The fact that it contains, coiled up in itself, millions of individual glands for carrying on this work, is sufficient to show the importance of the organ.
If all the little tubes of the sweat-glands in your body could be placed in a line, end to end, they would extend from twenty-eight to thirty miles. Think of that. Every one of us has in his own body nearly thirty miles of sewerage or drain-pipes for carrying off these impurities from the blood.
But how does this watery sweat, with its impurities, find its way from the blood into the sweat-tubes, and so to the skin? Every little sweat-tube, which opens on the surface of the skin, is coiled up into a ball at its inner extremity. It is this ball or coil of tubing which we really mean when we speak of the sweat-gland. Each gland is closely enveloped with capillary blood-vessels, and the walls of these vessels, as well as those of the tubes themselves, are so exceedingly thin as to afford an easy passage for liquids through them.
This passage of liquids through a membrane is called osmosis. It is best explained by means of an experiment as follows: Take a glassfunnel, with a long narrow tube, and bind a piece of thin bladder firmly over the mouth of it, so as to make it water- tight. Fill the funnel and part of its tube with a solution of blue-stone (sulphate of copper). Now place the funnel in a basinof water, so that the blue liquid in the tube and the water in the basin are at the same level.
Almost at once two things will happen. The liquid will begin to rise in the tube, and at the same time the water in the basin will be seen to gradually assume a blue tint. The explanation is that some of the water is entering the funnel, and some of the blue liquid is passing out into the water. This exchange goes on through the substance of the bladder itself; the two liquids have actually passed through the membrane. This is what we mean by osmosis, and this is the way in which the watery sweat, and all the impurities contained in it, are drained out of the blood in the capillaries. The coiled tubes of the little glands receive the sweat as it oozes through, and pass it outwards by means of the pores on the surface of the skin.
One very important purpose of the perspiration is to preserve the proper temperature of the body, so that it may not suffer from too great heat, whether from withinor without. The natural temperature of the body is from 98° to 100°F., and it never rises above this while the body is in a healthy state.
Imagine a person very much over-heated, either by some violent exertion, or through being compelled to stay in a heated atmosphere. In either case the skin at once begins to act very vigorously, and the body is soon bathed in perspiration. This perspiration rapidly passes off from the surface of the skin in vapor, and in doing so carries awayheat from the body, so that the natural temperature is still maintained.
You, no doubt, remember from some of our recent lessons that water can only assume the vapor form by using up a large amount of heat. The heat necessary in this case is derived from the body, and the withdrawal of that heat is Nature"s way of cooling the body.
These miles of drain-pipes having such important work to perform, it is in the highest degree necessary that we should assist them as much as possible, if we wish to keep our bodies in a healthy state. One of the best ways of assisting them is by keeping the body clean.
People who neglect their bodies, by not frequently washing them all over, often become the prey of loathsome skin diseases and various disorders. They allow the mouths of the glands to become clogged or choked up with dirt; and the poisonous waste-matters having no proper outlet, remain there and create disease. Therefore wash well andoften.
The skin should also be protected, as far as possible, from cold and damp. Perspiration is always going on, although we cannot always see the drops of liquid on the skin. This insensible perspiration, as it is sometimes called, must be allowed to go on without any interference. Therefore every care should be taken not to check the action of the glands by exposing the body to damp and cold for any length of time.
Remember, however, that this last piece of advice does not preclude the plentiful use of cold water on the skin. Never be afraid of cold water, provided that it is followed by a good rub down with a rough towel, to set the body in a glow again after the bath.
