CHAPTER I.

THE PHYSIOLOGICAL ACTION OF BATHS.

Since the influence of baths is exerted primarily upon the skin, and through the medium of the skin, upon the deeper-lying tissues and organs of the body, it is an absolute necessity for the reader at the outset to be made aware of the structure of the skin and its functions, as well as the relations which it bears to deeper-lying organs.

If the skin, say of the thumb, be looked at with a lens of moderate power, its surface is seen to be arranged in ridges and furrows, like a ploughed field; and at frequent intervals along the ridges are little depressions, which are known as the pores of the skin. These pores are the openings of the sweat ducts, and it is through these pores that the perspiration exudes. They are exceedingly numerous, and it has been calculated that there are as many as 2,800 to every square inch of surface, or about seven millions of them altogether. The ridges are seen to be divided into a series of minute hillocks, or _papillæ_, which are arranged in lines. These papillæ are the organs of touch, and are probably as numerous as the pores. They contain in their interior either loops of blood-vessels or nerve-endings.

These nerve-endings in the papillæ are of three kinds, which are readily distinguishable, and are known as tactile corpuscles, pacinian bodies, or end bulbs, according to the form which they take. Between the superficial and deep layers of the skin, the so-called cuticle and cutis, is a layer which partakes somewhat of the character of both. This is called the rete mucosum, and it is here that the pigment, found in the skin of the negro and in certain parts of the skin of white races also, is located.

Beneath the skin, in the subcutaneous tissue, are situated the sweat-glands, which are microscopical bundles of tubing, having one end running through the skin to terminate in the pores. These tubes are, or rather would be, if straightened out, about a quarter of an inch long; and it is estimated that the length of them in the entire body is about 28 miles! They pass through the upper layer of the skin or cuticle spirally, so that, although it is an easy matter for fluid to pass _out_, the passage in the opposite direction is by no means so easy. Each sweat-gland is plentifully supplied with blood-vessels, and is surrounded by a thin muscular coat, which is presumably able to exert, by its contraction, a certain amount of pressure, and so drive the secretions of the gland onward towards the pore, or external aperture.

The hair follicles, like the sweat-glands, are situated in the subcutaneous tissue. They are hollow receptacles, from the bottom of which the hairs grow. Alongside of each of these hair follicles is a pair of glands, called the sebaceous glands, which provide that small quantity of natural grease with which our hair is supplied. These glands resemble little bunches of grapes. The hair follicles are also furnished with a couple of small muscles, which, by their contraction, can cause a sensible erection of the hair. In certain parts of the skin there are glands which furnish a special odorous secretion. These are most plentiful in the arm-pits and between the toes. In the skin itself, and immediately beneath it, is a network of “lymphatic” vessels, whose function, it would seem, is mainly to drain the tissue of waste products. These vessels run towards the “lymphatic glands,” which, when enlarged, are often recognisable at the side of the neck, and which are very generally distributed throughout the body. In certain parts of the skin are special cells containing pigment.

Thus we see that the skin, which to the casual observer is an almost structureless membrane, is in reality a most complex and elaborate organ, richly supplied with blood-vessels, lymphatic vessels, and nerves, having its millions of papillæ and pores, and its miles of sweat-ducts. The hair follicles, with their sebaceous glands and muscles, are also to be reckoned by the million, and its odoriferous glands and special pigment-bearing cells probably by the thousand.

What are the various uses of this elaborate organ? In the first place, it serves as a protection to the softer parts beneath. Secondly, it serves to regulate the temperature of the body, by preventing, on the one hand, the too rapid radiation of the natural heat, and, on the other, by providing a very large surface for the evaporation of the constantly exuding perspiration, it prevents the overheating of the body. Thirdly, it is constantly removing from the body certain effete materials. These are the scales of the cuticle (which we remove whenever we wash and rub the surface), the perspiration, and the sebaceous, or greasy secretion. The amount of sweat varies immensely; it may be almost nil, or as much as a pint in an hour. The secretion of sweat is influenced by the temperature of the air, by exercise, by the drinking of fluids (especially warm fluids), and notably by the emotions. There can be no doubt that the secretion of a certain amount of sweat is necessary for perfect health; and it is the common experience of all that the checking of perspiration is very liable to be followed by dangerous internal congestion.

It has been demonstrated on some of the lower animals that, if the skin be shaved and varnished, death speedily ensues. This has been spoken of as a sort of cutaneous suffocation, death taking place owing to the charging of the blood with matter which should have been removed by the skin. It has been asserted, however, that death is due to cold in these cases; and it has certainly been demonstrated that animals so treated live much longer provided they be kept warm by a layer of cotton wool. Sometimes the skin is superficially destroyed by accidental burning or scalding, and it is well recognised that a burn or scald is dangerous to life in proportion to its superficial extent, rather than to its depth or severity.

The blood-vessels of the skin vary much in size under different circumstances, and the different degrees of pallor or redness of the skin are due to the condition of these superficial blood-vessels. The phenomenon of blushing is well known; and this should serve to remind us that the emotions can not only influence the amount of perspiration, but the size of the cutaneous blood-vessels. The intimate relations existing between the skin and the great nerve-centres should never be lost sight of.

The cutaneous blood-vessels enlarge in certain fevers, as scarlet-fever and measles; they can be made to enlarge also by the application of warmth, or irritants, such as mustard, or the stroke of a whip. Contraction of the blood-vessels is most marked in conditions of fear, or as the result of the prolonged application of cold.

Not only have the nerve-centres a great influence on the skin, but the skin is capable of exerting a great influence on the nerve-centres. This is not to be wondered at, when we bear in mind the myriads of nerve-bearing papillæ with which the skin is beset. When the soles of the feet are tickled, the legs are involuntarily moved; and when the arm-pits and sides of the chest are tickled, loud laughter is the result. These two phenomena are examples of what is known as _reflex action_, i.e., the tickling produces an effect upon the nerve-endings in the skin, and this effect travelling to the nerve-centres (the spinal cord or brain) is _reflected_ to the muscles, and produces movement of the leg or laughter. When the body is suddenly immersed in cold water, a not uncommon result is a shivering and a chattering of the teeth; and when cold water is sprinkled on the forehead or chest, deep inspiration and a catching of the breath is produced. These are examples of “reflex movements,” due to impressions made upon the nerves of the skin; and since many of the results of bathing are undoubtedly due to this kind of reflex action, it is very important to bear it constantly in mind. The connection between the nervous centres (the brain and spinal marrow) and the skin is shown also in the occurrence of what is known as goose skin, or _cutis anserina_, which is caused not only by the application of cold to the surface of the body, but even more readily by the mental states which make the “Hair of our flesh stand up.” The rationale of this phenomenon is the contraction and shortening of the little muscles which we have seen to be in intimate relationship with the hair follicles. There can be no doubt also that the pigment cells, which are scattered thinly throughout our skins, are subject to the control of the nervous centres, and it is well known that the tint of the complexion will sometimes vary with emotional states, as it certainly does with physical states. These considerations are sufficient to show that the skin plays a most important part in the animal economy, as a protective, a secreting, a vascular, and a nervous organ.

An all-important point to be determined with regard to the skin is its power of _absorption_--that is, its power, if any, of allowing substances to pass through it, and so reach the interior of the body. It is well ascertained that, if the surface of the skin be broken, absorption takes place with great rapidity, and that even when the skin is not broken, it is comparatively easy to get absorption of certain matters, such as mercurial ointment or extract of belladonna, provided they be applied with a certain amount of friction. We saw that the ducts of the sweat-glands perforated the skin spirally, and the friction has the effect of opening the mouths of these little ducts, so that the greasy or sticky preparation gets lodged within them and absorbed.

It has been proved with tolerable certainty that gases, such as carbonic acid and oxygen, are capable of penetrating and permeating the skin in small quantities, but it is extremely doubtful if water is ever absorbed through the skin. It has been attempted to settle the question by weighing the body before and after a prolonged immersion in the water, but such experiments are so beset with fallacies that they are almost worthless. The fact that shipwrecked sailors are in the habit of successfully lessening their thirst by immersion of the body in water, or by wetting their clothes, is well known, but this effect may be due to the arrest of the cutaneous evaporation, or by an effect upon the nerves.

At all events it seems safest, in the present state of our knowledge, to assume that water is not absorbed through the skin; or if it be, that it is absorbed in such extremely small quantities that the effect of baths can in no sense be due to the absorption of the water in which the body is immersed. As to the absorption of the various salts contained in sea-water or mineral waters, there is no evidence whatever that these are ever absorbed even in the most minute quantities. If the salt dissolved in sea-water were absorbed through the skin, it is tolerably certain that sea-bathing, far from being the luxury which it is, would be regarded as a highly dangerous and most unpleasant practice.

Baths of all kinds serve, or may be made to serve, as vehicles for temperature, and by their aid we are enabled to surround the body with a temperature which is different to its own. Before we can fully understand the effect of hot and cold baths on the economy, it is necessary to enter into some discussion of the nature and source of the natural heat, of the body. The natural heat of the human body is between 98° and 99° of Fahrenheit’s scale; and this temperature, roughly speaking, is uniformly maintained by the healthy body under all the varying circumstances to which it may be subjected. In the arctic regions, and in the tropics the temperature of the body rests at 98·6°; or, if variations occur, they are so slight in amount as to be hardly noticeable. In a cold atmosphere, therefore, the body has the power of maintaining its heat; and in a warm atmosphere it is equally able to maintain its coolness. This is a remarkable fact, and is due to the power possessed by the human body of adjusting the production and loss of heat. Heat is produced in the body by the combustion of food and tissues, exactly as heat is produced in a fireplace by the combustion of coal. The amount and rapidity of this combustion necessarily varies with the amount and nature of the food consumed and the activity of exercise and other vital processes. The most active tissue in the body is the blood; through its agency most of the combustion processes are carried on, and by its rapid circulation to all parts of the body the most distant points of the human frame are kept at the same temperature. The temperature of the blood is due to the amount of combustion taking place in the tissues, and the amount of combustion taking place in the tissues is due to the amount and energy of their blood supply, which last depends upon the force of the heart’s action and the size of the blood-vessels which have the power of contracting and dilating, and which are subordinated to the regulating influence of the nerve-centres. If that part of the nerve-centres (the upper part of the spinal cord) which controls the size of the vessels be injured or destroyed, the combustion processes going on in the body seem to get beyond control and the temperature may be dangerously increased or decreased, the exact reason of one or the other phenomenon not being known. The limits of body temperature which are compatible with life are not very wide; for if the temperature rise to 109° or sink to 76° death will inevitably result, and a rise or fall of 7° from the natural temperature is decidedly dangerous. Seeing how narrow are the limits of temperature within which life is possible, we cannot but be amazed at the marvellous arrangements for maintaining the normal level of animal heat. The body is cooled by the evaporation going on from the lungs; by the more important evaporation going on from the skin (every one who has covered a portion of the skin with spirit and has encouraged its evaporation by blowing upon it knows practically the cooling effect of evaporation), and by the radiation of heat from the surface of the body, and the conduction of heat from the body by things in contact with it.

The _immediate_ effect of a cold bath is to chill the _surface_ of the body, the temperature of which, as tested by a thermometer, may fall several degrees. At the same time there is produced a pallor of the surface and goose-skin. While the surface is cooled, however, the blood itself undergoes an increase of temperature, due to an increase of the combustion processes going on in the body, of which we get additional evidence in the increase of the rate of the pulse and respiration, and an augmented discharge of carbonic acid from the lungs. There is a sudden sense of chilliness, and this impression, made upon the nerves of the skin, produces, by its action on the brain and spinal cord, some slight mental excitement and shivering of the limbs. After the bath has been continued some little time the temperature of the blood falls (sometimes as much as three or four degrees), the pulse and respiration get slow, the shivering gives place to lassitude, and the mental excitement to listlessness. On removal from the bath the phenomenon of “reaction” sets in. The vessels of the skin enlarge, the chilliness gives place to warmth, and the feeling of uneasiness is succeeded by a sense of comfort. This reaction follows most quickly when the bath is of short duration, and when its effects are suddenly induced. The shorter the bath the less is the ultimate depression of the temperature of the blood. The shorter the bath the greater is its power of _stimulating_ function; the longer it is continued the greater is the effect of _cooling_.

The effect of a _warm_ bath is to raise slightly the temperature of the surface and the temperature of the blood. The pulse and respiration are both quickened, and the escape of carbonic acid from the lungs is also increased. The blood-vessels of the skin get dilated, and the surface is reddened in proportion to the heat of the water. Warm baths of a moderate temperature can be borne for a longer time than cold baths; but if the temperature be too high, and the bath too long-continued, faintness is liable to occur. On removal from the hot bath the skin is in a very delicate and susceptible state, and the vessels are liable to “re-act” in the direction of extreme contraction, in which case dangerous internal congestion may occur. If, however, the skin be protected, and the patient be placed in a warm room, or in bed, a violent perspiration will ensue. In the cold bath the muscles are liable to become stiff; but in the warm bath a stiff and fatigued muscle will resume its suppleness. After a hard day’s hunting a warm bath is a well-known and agreeable luxury.

The phenomenon which is popularly known as “reaction,” and which occurs after both hot and cold baths, is a most remarkable one, and seems to show that our bodies resent any interference with their function. Thus experiments have shown that if the temperature of a healthy man be raised or depressed by any artificial means, such as hot or cold baths, the subsequent reaction in the direction of the depression or exaltation of the temperature is such that the mean temperature of health is accurately maintained. A German observer, Jurgensen, found by a series of accurate observations on a patient who submitted to a series of baths of a temperature of 50° Fahr., each bath lasting twenty-five minutes, that notwithstanding the rapid abstraction of heat, which gave rise to shivering, lasting for several hours, the diminution of bodily temperature which occurred during the bath was followed, after an interval of four or five hours, by an elevation which precisely compensated it, so that the mean normal temperature was maintained in spite of the interference of the physiologist.

It will have been observed that the ultimate result of both hot and cold bathing, if conducted in moderation, is about the same, viz., an increased circulation of blood through the skin. In both cases also, the combustion going on within the body is increased, as evidenced by the escape of an increased quantity of carbonic acid from the lungs. In the case of the cold bath, this increased combustion is due to the stimulating effect of the cold water, while in the hot bath it is due to the artificial heat facilitating the natural combustion processes of the body. The effects of the hot and cold bath upon the combustion processes going on in the body may, not inaptly, be compared to the effect produced upon a furnace by the hot and cold blast, both of which encourage combustion and increase the heat given off by the furnace; but the hot blast so facilitates combustion that the same work is done by its aid, with an expenditure of 2-1/2 tons of coal, that is done by the cold blast with an expenditure of 8 tons of coal. If we want a fire to burn well, we have several courses open to us; the first is to poke it, which may be regarded as simple stimulation; the second is to supply it with a cold blast, in which case we supply large quantities of oxygen, but at the same time counteract the heating effect by the coldness of the blast. By employing a hot blast, the combustion is facilitated without any counteracting chilling. By each of these methods we hasten the ultimate extinguishing of the fire, unless fresh fuel be added. The employment of the hot blast entails the most economical use of the fuel.

It has been said, with regard to the use of baths, that _cold stimulates, but heat facilitates function_. “Between the two therapeutic opposites,” says Braun, “a similar relation exists, as between winter and summer life, and between sea and mountain air. The physician who has, to a certain extent, acquired an insight into the diseased side of mankind, divides the chronically sick into two groups, the one consisting of individuals whose organism has sufficient capital to afford the strong reaction required, the other consisting of persons needing nice management, and whose own power cannot be exposed to any great demand. For the one there is the system of exercise, cold treatment, cold baths, sea baths, and sea air; for the second, indulgence, warm treatment, warm climate, warm baths, mountain air.”

Seeing that both hot and cold baths increase the natural combustion of the body, it will be evident that persons undergoing a course of treatment by either method should be exceedingly careful that during the progress of their course of treatment the best fuel only is placed on the human furnace. They should eat the simplest and most nutritious food, and breathe nothing but the purest air.