PRACTICAL HYDROTHERAPY by C. E. Stewart

Seventh-day Adventist Publishing Association · Battle Creek, Mich. · Feb 25, 1902

PRACTICAL HYDROTHERAPY.

By C. E. Stewart

Lesson 2. — Some Principles of Physiology.

C. E. STEWART, M. D.

In our last study we dealt largely with the nervous system, and incidentally called attention to the importance of the skin as a medium in which impulses which have a marked influence in modifying the various functions of the body, are generated. In this connection it will perhaps be profitable to outline in a brief manner the essential facts pertaining to the anatomy and physiology of the skin, so that we may more clearly understand why it is that in the application of hydriatic measures to the skin, such wonderful results are obtained in the treatment of disease.

The adult man of average size has about seventeen square feet of skin, averaging about one eighth of an inch in thickness, and consisting of two parts: the outer, called the epidermis, or false skin; and an inner, the dermis, or true skin. The outer layer contains no blood vessels or nerves, and serves principally as a protective covering for the true skin, which contains blood vessels, nerves, sweat and sebaceous glands, yellow elastic and white fibrous tissues, involuntary muscle fibers, fat, and lymphatics. The hairs extend through the outer layer into the deeper parts of the true skin, where they receive their nourishment; the nails are likewise a part of the skin. The sweat glands, which are very numerous,—about 2,500,000 in all,—play an important part in the maintenance of health. They are very energetic, and secrete about two pints of fluid upon the surface of the body daily. Each gland is supplied with a blood vessel and several sympathetic nerve fibers.

The functions of the skin are chiefly those of sensation, protection, secretion, excretion, and regulation of temperature. As an organ of sensation the skin plays a very important rôle, because its nerves are capable of responding to a great variety of stimuli. By means of it we can detect whether an object is hard or soft, whether it is hot or cold, and whether it produces pain or pleasurable sensation. No matter what the character of the stimulus is, the impulse it produces is conveyed to the spinal cord and brain.

As an organ of protection the skin prevents the delicate underlying structures from injury; and the fact that the outer layer is tough and horny is of great service in this direction, especially in the palms of the hands and soles of the feet.

As an organ of secretion and excretion it acts by means of the sweat glands in secreting a considerable amount of fluid from the blood which contains waste matter from the tissues, and in excreting it upon the surface of the skin. There is a reciprocal relation existing between the skin and the kidneys; the more fluid excreted by the skin, the less by the kidneys, and vice versa. In winter the skin is less active, while during warm weather the opposite condition exists. This is a very important fact, and one which should not be forgotten; for in many cases where the kidneys, on account of disease, cannot perform their normal functions, the skin, by increasing the activity of the sweat glands, may be made to eliminate much of the fluid and waste material that is ordinarily excreted by the kidneys.

As a regulator of temperature the skin holds an important position. It equalizes the temperature by the evaporation of the moisture, which is excreted from the sweat glands upon its surface, and by radiation and conduction. Of all the heat given off from the body, 88 per cent passes off through the skin; of this amount 73.5 per cent is by radiation and conduction, and 14.5 per cent by evaporation. In order that the skin may perform its functions in a proper manner, it is necessary that it should be kept clean by frequent bathing. Unless this is done, the oily material which comes from the sebaceous glands of the skin, together with the solid matter of the perspiration remaining after the evaporation of the fluid, and other foreign material which is constantly accumulating on the skin, closes up the orifices of the perspiratory and sebaceous glands, and thus interferes with the elimination of the wastes of the body, the retention of which has a very deleterious effect upon the system. Through the influence of the elastic tissue and muscle fibers contained in the skin, it has the power of contracting thereby lessening the amount of fluid—both blood and lymph—contained in it. On account of this lessened amount of fluid, the skin is rendered less conductive, consequently less heat is eliminated.

When the skin is cooled, either by coming in contact with a cold atmosphere or by an application of cold to the surface, one will observe that the skin becomes roughened—goose-flesh appearance—and bloodless. These phenomena are all due to the influence of cold upon the sensory nerves of the skin, which carry impulses to the spinal cord and the brain, where it is recognized that the body is becoming cooled too rapidly; consequently other impulses are started from the centers to the skin, causing the muscles, blood vessels, etc., to contract in order that the heat of the body may be conserved and as little eliminated as possible; at the same time the part of the nervous system which has to do with the regulation of heat within the body, conveys impulses to the heat-generating tissues, which at once proceed to manufacture more heat, in order that the normal temperature of the body be maintained.

If instead of the skin being brought into contact with a cold atmosphere, it is brought into contact with one much warmer than itself, the opposite conditions will result,—the skin will become more or less relaxed, the color will become reddened on account of the increased amount of blood flowing through the skin, the sweat glands will also become more active, and through the evaporation of the moisture a more uniform temperature will be maintained. The more fluid there is evaporated, the cooler the skin becomes; this may be practically demonstrated by moistening the skin over the back of the hand or a finger, and then blowing upon it, or by allowing the wind to strike the moistened surface; the cooling noticed will be very appreciable; the test is so delicate that it is often used to ascertain from which direction the wind is blowing.

We will now turn our attention to the study of the production of heat within the body. Every one is aware of the fact that the heat of the body must be maintained by heat generated within itself, and the query very naturally arises, How is this heat generated? Like all other functions of the body, that of heat production is under the control of the nervous system. The heat mechanism, as we are pleased to term it, consists of thermogenic (heat generating) nerves, thermogenic centers, and thermogenic tissues. The thermogenic centers are of three kinds: the thermo-accelerator, or heat increasing; the thermo-inhibitory, or heat diminishing; and the automatic, or governing, centers. The first two are located in the brain, and the latter in the spinal cord. The thermogenic tissues are the ones in which the heat is produced, the principal ones being the muscles and the large organs, such as the liver, lungs, heart, etc.; in fact, some heat is produced wherever there is vital activity. A dead body is of the same temperature as the surrounding atmosphere, while the temperature of a living body is independent of the temperature of its surroundings. On account of this fact, the term “vital heat” has been used to designate the heat generated within the body. The same life which performs all other bodily functions also causes the formation of the heat.

The source of vital heat is found in the food eaten; not that the food as such conveys heat to the body, but that it contains within it the principles which may be changed to heat. During the digestion, absorption, and assimilation of food, chemical changes are constantly taking place, and are accompanied with the liberation of heat. The greatest amount of such chemical changes takes place in the muscles, and as the muscles make up the greatest proportion of the bulk of the body, most of the heat is produced in them. We also find a great deal of chemical change going on in the liver and other organs which are active; in fact, there are of necessity chemical changes going on wherever there is vital activity.

The thermogenic centers and nerves have for their function the controlling of the amount of chemical change which takes place in the thermogenic tissues. The centers in the spinal cord act as governors, and can control the equilibrium up to a certain point; but when it gets beyond their reach, as in fevers or under abnormally cold surroundings, the inhibitors and accelerators are called upon. When too much heat is produced, the inhibitory centers send out impulses which cause a depression in the heat-producing tissues, and at the same time the blood vessels of the skin dilate, the heart beats faster, and the sweat glands pour forth their secretion more abundantly; all of which helps to eliminate the excessive amount of heat being formed, and in case the increased heat elimination keeps pace with the increased chemical changes no rise will result; but, on the contrary, if less heat is eliminated than is produced, a rise of temperature will result.

In case the skin becomes cooled to such an extent that the centers within the cord cannot, through their influence, cause a corresponding increase in heat production, the accelerator centers are called upon, and they send impulses to the thermogenic tissues, which cause increased chemical changes, resulting in increased formation of heat. These increased chemical changes result from increased activity, and this is frequently noticed in the case of shivering which follows the contact of cold with the skin. A chill is always followed by a rise of temperature. The dog shivers to get warm. In case the amount of heat produced is equal to the amount of heat abstracted by the cold, no change of temperature will result; however, if the amount of heat withdrawn is greater than the amount produced, there will be a fall of temperature. These facts have a practical bearing upon the treatment of disease, especially fevers. By means of water of different temperatures heat production and heat elimination may be readily influenced.