In another part of this work we have attributed to the kidneys a very important part in the causes of premature old age, as their degeneration is one of the most striking causes of auto-intoxication, the immediate cause of old age. The more injurious the products passing through the kidneys, the quicker will these noble organs be degenerated and the sooner will they decay.

It will thus be the wisest policy in the prevention of premature old age and in the interests of a long life, to lighten the work of the kidneys, and avoid their being overstrained by throwing a part of the work on their partner—the skin. This organ, as stated at the close of the preceding chapter, is, in a certain measure, a co-partner with the kidneys. When, through cold weather, for instance, the functions of the skin are diminished, a greater flow of liquid will pass through the kidneys in the form of urine; but when the weather is hot and there is perspiration, to a certain extent, less liquid will be secreted and excreted by the kidneys: that is, they will work less. By perspiration, also, more common salt will pass through the skin, and consequently less through the kidneys.

It follows logically from these considerations that if we are anxious to preserve the vitality of the kidneys and also free the blood from noxious elements, we must pay special attention to a good action of the skin, and this is only possible by a rational hygiene.

The sudorific glands are abundantly provided with small blood-vessels, which bring a large quantity of warm blood to them, from which they absorb watery and solid parts, and, in all probability, gaseous substances also, and pass them through their tortuous excretory channels to the surface of the skin. The mouths of these channels are the pores, and it is of fundamental importance that they remain open; for if closed these waste products cannot pass out and must remain in the body, while in addition no air can pass into the pores, and so no exchange of materials can take place.

These pores can easily be clogged; for example, by the scales—cuticle—which we shed every day, mostly from the superficial layers of the skin, and also by the oily secretion of the sebaceous glands. The fat that these glands secrete is intended by Nature to serve as a protection against liquids, like water, and against the perspiration from the skin. In some persons this fat is secreted in too large quantities and may then, especially with its products of decomposition, clog the pores. In the same way the products of perspiration, and also foreign materials, such as dust, may close the pores. It will, therefore, be necessary to remove all these substances which are preventing the proper aëration of the skin and the elimination of harmful matters by it. It is also not impossible, when the products of decomposition of the sweat remain long in close contact with the skin, that some of those injurious elements may be re-absorbed.

The best method of getting rid of these harmful substances is by bathing every day. But water alone, except it be very hot, and the bath of long duration (and in this case it presents some inconvenience and may be injurious also to health if taken daily), is not able to remove the oily and fatty products of the skin. Therefore it is best to use soap in addition to water, and to rub energetically with it the entire skin surface of the body.

Besides removing, by a bath, the injurious products that clog the pores, we must take particular care to allow air to penetrate to the pores as freely as possible, thus permitting a free issue to the body exhalations and facilitating respiration by the skin.

We should not, therefore, exclude the air by thick, non-porous clothing, such as furs; nor should we use underwear that fits too closely to the body. To permit of a thorough aëration of the skin it would be advantageous to remain exposed naked to the air once or twice during each twenty-four hours, and each time for at least five to ten minutes. When the weather is warm and we bathe in the sea or a river, we combine the advantages of a water and air bath. But in places where there is no sea, lake, or river in which to bathe, we could, if living in the country, enclose some spot for such an air bath which, in sunny weather, would also become a sun bath at the same time. On the grass of a clearing in a wood, or in a garden, such an air bath could best be taken. In summer, if the air is not too warm, and if we are in the sun, we may remain longer than ten minutes in such an air bath.

If we are not able to procure a place in which such a bath can be taken quite naked without being seen, the next best thing is to clothe oneself in amply large white pajamas, or, for women, in a very wide white mantle or costume of the empire style, and thus attired to take a walk in the garden or ground of one’s property.

In cities many can take such an air bath in one room every day when they can spare ten minutes, the best time being before dressing and after undressing. But also during the day, especially in summer, we should spare a few moments to take such a bath. In winter the room must, of course, be warmed for the purpose. In combination with the bath, breathing exercises can also be performed to great advantage in the way described in the chapter on the advantage of open air. In order to avoid catching cold in such an air bath it is advisable to rub the entire skin surface of the body. This causes much blood to be brought to the skin; thus more blood is conveyed to the sudorific glands which are thereby enabled to absorb a larger quantity of harmful matters from it, while at the same time more air can be taken in by the pores. While rubbing—which is best done by a brush—we can also move about, and while standing also beat the periphery of the body with a thick rough towel in the same way as in Finland they do with brushwood after hot baths. It is not painful and is very effective in producing a hyperæmia of the surface of the skin. When the skin is thus better nourished with blood it also offers more resistance to germs that may cause diseases of the skin, and such better nutrition and its improved hygienic condition is a safeguard against catching cold.

Such an occurrence is more likely to occur in persons who neglect a thorough cleansing of the body daily by baths and who go warmly clad; in such cases the muscles which contract the pores are less active, and because of this more body heat is lost and catching cold more easily takes place. When we feel warm more blood circulates through the skin, and when afterward cold air reaches us the pores, in a normal person, contract quickly and the blood is retained in the interior of the body. Thus we are prevented from giving off too much warmth from the body and catching cold. Persons who have been trained since their early childhood to cold water and cold air show a great facility for reaction against cold. When cold air reaches the skin, which on account of warm surroundings has become warm, filled with blood, red, and moist, the skin will contract and become pale, the easy conduction of warmth will be checked, and the heat retained in the body. Thus such persons will not so easily catch cold as others whose skin is not kept in good hygienic condition.

Many people have already shortened their existence by catching colds. Pneumonia, pleurisy, nephritis, and many other dangerous ailments have arisen from such a cause and led to premature death. A good hygiene of the skin not only serves to eliminate toxic products from the body and keep our kidneys in good order, but also prevents the tendency to catching cold, which is so often the cause of an early death. We must, therefore, do our best by a careful rational attention to the hygiene of the skin, and for this purpose we will deal further with the subject in two chapters on the hygiene of the skin by bathing and by rational clothing.