The uses of water in health and disease

by John Harvey Kellogg

The number of these delicate glands is enormous. It has been carefully estimated to be about 2,300,000 in a single individual. The length of each is about one-fifteenth of an inch, making their aggregate length about two and one-half miles.

The Mucous Membranes.—All cavities in the body which communicate with the surface by openings are lined with a membrane which is called mucous, from the character of its secretion. The mucous membranes are continuous with the skin at the natural openings of the body, and very closely resemble it in structure, being formed of several layers, like the skin, and having a superficial portion made up of layers formed by the deeper tissues. Mucous membrane forms the lining of the air-passages and lungs, of the whole alimentary canal, and of the urinal and genital organs. Its extent in the lungs alone has been estimated by scientists at 1400 square feet, or more than seventeen times the whole extent of the skin.

Functions of the Skin.—The skin performs a number of very important offices for the body. Perhaps the most important is that of excretion. Each of its millions of sweat glands is actively and constantly engaged in separating from the blood impurities which would destroy life if retained. These foul products are poured out through a corresponding number of minute sewers, and deposited upon the surface of the body to the amount of several ounces each day, or several pounds, if the whole perspiration be included in the estimate, as is commonly done.

The skin is also an organ of respiration; it absorbs oxygen, and exhales carbonic acid gas, with other poisonous gases. The amount of respiratory labor performed by the skin is about one-sixtieth of that done by the lungs. In some of the lower animals, the whole work of respiration is performed by the skin. In the common frog, the respiratory action of the skin and of the lungs is about equal.

Another important office of the cutaneous tissue is absorption. The absorption of oxygen has been already referred to; but it absorbs liquids as well as gases, and to a much greater extent. By immersion in a warm bath for some time, the weight of the body may be very considerably increased. Dr. Watson, an English physician of note, reports the case of a boy whose weight increased nine pounds in twenty-four hours solely by cutaneous absorption of moisture from the air. This extraordinary action was occasioned by disease. Seamen, when deprived of fresh water, quench their thirst by wetting their clothing with sea-water, the aqueous portion of which is absorbed by the skin. The lymphatic vessels are believed to be the principal agents in absorption.

Another remarkable function of the skin is the regulation of temperature. By its density and non-conducting property it prevents the escape of necessary heat to a considerable degree. But when the amount of heat generated in the body becomes excessive, either from abnormal vital activities, or by exposure to external heat, the skin relieves the suffering tissues by favoring the escape of heat. This desirable end is attained through the evaporation of the moisture poured out upon the surface by the perspiratory glands.

It has been estimated that the evaporation of water from the cutaneous surface and the mucous membrane of the lungs occasions the loss each minute of sufficient heat to raise a pint of water 100° F. in temperature. This is certainly a powerful cooling process.

Lastly, we mention as a further function of the skin, and one which is not the least in importance, its utility as a sensitive surface. It is a well-established physiological fact that the mind is only a reflection of impressions received from without, or at least that its character is largely determined by the nature of the impressions made upon its organs of sensibility. The skin is the organ of touch, and the various modifications of tactile sensibility. It is the most extensive organ of sensibility in the body, and is very closely connected with all the great nerve centers, so that it is perhaps the most efficient means through which to affect the general nervous system. Its intimate sympathy with internal organs is shown in a great number of diseases in which this organ evidently suffers on account of disability of some other one.

Functions of the Mucous Membranes.—The functions of the mucous membranes are strictly analogous to those of the skin. Like the latter organ, a mucous membrane excretes and absorbs. It eliminates foul matters, and absorbs useful substances in a fluid state.

The importance of the functions of the skin is shown by the fact that a person quickly dies when its action is interrupted. A coat of varnish or caoutchouc, applied over the whole skin, will kill a man almost as quickly as a fatal dose of strychnia. In experiments upon animals, horses, dogs, and other animals have been killed by obstructing the action of the skin by some similar means. A little boy was once killed by covering him with gold leaf to make him represent an angel at a great celebration.