CHAPTER VII. The Skin-Its structure and uses- -Its functions essential to Life. THE vital functions of the Skin, in their relation to the animal economy, were formerly greatly underrated, because not properly understood. The investigations, however, of modern physiologists, aided by powerful miscroscopic agency, have clearly revealed its truly wonderful organism, and demonstrated how all-essential its sound and active vitality is to the due performance of the functions of healthy life, and also how it is designed as a medium through which, in cases of disease, the internal organism can be safely reached and acted on. The Skin, in the popular acceptation of the term, is considered as only one simple substance, but in reality what in ordinary language is called the skin, is to the physiologist known as the epidermis, the outer, or scarf skin, underneath which lies the cutis vera, or true skin. Thus, properly speaking, the skin consists of two layers, the inner layer, and, immeasurably, the more sensitive and delicate being known as the cutis vera, the derma or true skin, and the outer layer, by which the cutis is protected, as the epidermis or scarf skin. Between these two layers, or strata, there is a soft granular or cellular substance called the rete mucosum, which contains the particles that give colour to the skin. Some physiologists hold that the matter which gives colour to the skin is situated in the rete mucosum, while others are of opinion that it lies in the inner or flocculent surface of the epidermis. According to Dr. Beddoes, chlorine gas will extract the colouring matter from the negro; and Fourcroy verified this experiment, but in a few days the black colour returned again with its former intensity. "The skin," says Carpenter, is concerned in two great classes of changes; the excretion of various matters from its surface, and from the glandulæ in its substance; and the reception of impressions upon the nerves, with which it is so copiously supplied." Thus the skin performs analagous functions to the lungs, in so far as it takes in and gives out similar matters which are taken in and given out by the lungs, and for this reason it has been described as "the assistant apparatus of the lungs." In health the skin is the seat of various secretions which seek the surface of the body to be eliminated as excrementitious and deleterious matter from the system. These secretions are collected in small glandular organs which are seated just beneath the cutis, or true skin, and are diffused over the whole surface of the body to an extent that is truly marvellous. From these glandular organs innumerable minute tubes, popularly called "the pores of the skin," convey the secretions through the epidermis, or outer scarf skin, to be exuded in sensible or insensible perspiration. When nature has destined the pores to perform such an important office, it can be readily understood how essential it is to health that the normal action of the pores should not be obstructed. This becomes more clearly apparent when we consider the minute organism of the skin, and the marvellous system of pore sewerage which nature has provided for the healthy maintenance of human life. Erasmus Wilson, the eminent Anatomist and Physiologist, in his Practical Treatise on Healthy Skin, says: "To arrive at something like an estimate of the value of the perspiratory system, in relation to the rest of the organism, I counted the perspiratory pores on the palm of the hand, and found 3,528 in a square inch. Now, each of these pores being an aperture of a little tube of about a quarter of an inch long, it follows that in a square inch of skin on the palm of the hand there exists a length of tube equal to 882 inches, or 73 feet. Surely such an amount of drainage as 73 feet in every square inch of skin, assuming this to be the average for the whole body, is something wonderful, and the thought naturally intrudes itself—What if this drainage were obstructed? Could we need a stronger argument for enforcing the necessity of attention to the skin? "To obtain an estimate of the length of the tube of the perspiratory system of the whole surface, I think 2,800 might be taken as a fair average of the number of pores in a square inch, and 700, consequently, of the number of inches in length. Now, the number of square inches of surface in a man of ordinary height and bulk is 2,500; the number of pores, therefore, 7,000,000; and the number of inches of perspiratory tube 1,750,000; that is, 145,833 feet, or 48,600 yards, or nearly 28 miles."Page 43. Now, the secretions of the human system are constantly going on, and in a normal, or healthy state of the body the por-tion designed to be exhaled by the skin is carried off imperceptibly by the pores. The entire amount of fluid thus insensibly evaporated by the pores, is estimated at eleven grains per minute, while the lungs so sensibly in motion and apparently more active, only evaporate about seven grains. Carpenter says, "there is reason to believe that at least 100 grains of azotised matter are excreted from the skin daily," consequently any cause which checks this excretory power of the skin must necessarily throw an additional and unnatural amount of labour on the other excretory organs of the system, and thereby tend to produce a derangement of their functions and cause disease. According to Dr. Thudichum, "the secretions of the human skin may be divided into volatile and solid, the former consisting of-1. Carbonic acid; 2. Water; 3. Some volatile acid, not yet accurately determined; and the latter of 1. Urea; 2. Chloride of sodium; 3. Fatty matter; 4. Earthy salts of some fatty solids; 5. Small quantities of some other alkaline salts.". Phosphates and salphetes, always present in any other secretion, he has not, he says, ever found in perspiration. Thus while the excretions of the skin are analagous to some extent to those of the lungs and kidneys, they are not entirely so, but its dignity as an excretory organ becomes more apparent from a study of the quantities of matter discharged by the several organs; for while the lungs in 24 hours discharge fifteen ounces of volatile matter, the skin discharges thirty ounces, so that two-thirds of all volatile excretions pass by the skin. An almost equal weight of water leaves the body through the kidneys, charged with matter peculiar to that secretion. can thus understand how it is that the suppression of skin action becomes a fatal source of disease. But as Erasmus Wilson observes: "It is not as an emunctory or purifier only that we must regard the skin; its influence and power have a wider range of action in the maintenance of health. Besides comprehending a vast system of drainage tubes, which open on the surface by seven millions of pores, besides, also, a wonderful and perpetual labour, by which the skin is drawing from the blood certain organic elements in the fluid state, and converting them into solid organic formations, which are known as cells and scales, these cells and scales being the tesselated mosaic with which the skin is furnished upon the surface, so as to render it capable of existence in the external world; besides this and much more, the skin is converted into a kind of sponge by the myriads of blood-vessels which enter into its structure-bloodvessels that many times in an hour bring the whole-aye, every drop-of the blood of the body to the surface; bring it that it may furnish the materials for the microscopic pavement; that it may be purified by the abstraction of its unwholesome principles; that it may breathe the vital air of the atmosphere without;-besides this, also, the skin near its surface is one vast network of nerves-nerves, mysterious organs, that belong in their nature to the unknown sources of the lightning, the electric currents of the universe. And besides these, again, there is every variety of animal tissue and contrivance by which all this apparatus is held together and maintained in the best state and position to ensure its safety and perfection. In truth, the contemplation of the structure and functions of the skin, when viewed with the eyes of the mind, is almost overwhelming; and the words of the poet break upon our memory— "In human works, though labour'd on with pain, Yet serves to second, too, some other use." "One word more as to the importance of the skin in the animal economy, and that word a summary of its functions and principal vital attributes. The skin is a sanitary commissioner; draining the system of its impurities; it is an energetic labourer, in that perpetual interchange of elements which, in its essence, constitutes life; it is a regulator of the density and fluidity of the blood; it performs the office of a lung in supplying the blood with oxygen, and abstracting its carbon; it changes the crude organic elements of the blood, so as to render them capable of nutrition; it emulates the heart in giving speed to the circulating blood; it is the minister of the brain and spinal marrow in its properties of sensation; and it feeds and nourishes, and keeps in the highest operative condition, that part of the nervous system which is confided to its care. "Viewing the skin in this way, and recognising its just claims to consideration as an important animal organ, we are led to the conclusion that the skin is a part of the digestive system, like the liver and kidneys, by virtue of its emunctory and nutritive powers; it is an appendage of the heart, and a part of the system of the circulating of the blood; it is a surface lung, a breathing organ; and it partakes of man's intellectual nature by its close connection with, and dependence on, the brain. In the lower animals, the skin combines in itself alone, the feeling, seeing, smelling, hearing, and judging organ."-The Eastern or Turkish Bath, &c., p. 113, &c. From this it will be perceived how vitally essential a sound condition of the skin is to the enjoyment of good health. When its functions are imperfectly performed, the whole body necessarily suffers. The heart, the lungs, the liver, the stomach, the brain, the nerves, the bowels, are imperfectly nourished, and their vitality is moreover oppressed and weakened by the noxious matters with which the blood is loaded. Thus a weight is placed on the very springs of life, while it is only by restoring the healthy action of the skin that this weight can be taken off. We have further proof of the importance of skin action to Life in the fact, that if an animal is coated over with a varnish impervious to air, by which means the functions of the skin become impeded, and its organism, as it were, paralysed, death in a few hours would be the inevitable result. This has been demonstrated by repeated experiments on the lower animals; it is also true in the case of man. Close the pores of his skin by a similar coating, and congestion of the internal organism would take place, resulting sooner or later in death. There is a case recorded of a young boy who was covered over with a coating of gilt, to represent the Golden Age, at a pageant given by Pope Leo X., and the effect was that, by thus unconsciously impeding the functions of the skin, death ensued in a few hours.. It is an irresistible conclusion, therefore, in which all eminent Physiologists agree, that whatever interferes with or impedes perfect skin action, must be more or less detrimental to health, and calculated, of necessity, to engender disease. "When |