There are some two and a half million small glandular formations—the sudorific glands—on the whole surface of the body in the subcutaneous tissue of the skin, from which issues a secretory tube somewhat of the nature of a corkscrew to the external surface of the skin.
These glands are richly provided with blood-vessels, and a comparison may be drawn, to a certain extent, between the glomerules of the kidneys and these small glandular formations. The first receive certain substances from the blood and give it off through the tubules which carry away the urine, and the latter take both fluid and solid substances from the blood and eliminate it in the form of sweat through the excreting channels of the sudorific glands.
Gas can also be eliminated through the skin—carbonic acid—though in infinitely smaller quantity than by the lungs, for while the latter eliminate from 800 to 1200 grammes of carbonic acid, it has been shown by the experiments of Aubert[232] that a human being eliminates through the skin a maximum of 6.3 grammes and a minimum of 2.3 grammes in twenty-four hours, which is certainly a very small quantity. Besides carbonic acid the skin probably also eliminates other organic combinations in the form of gas, though it would be very difficult to analyze them by exact experiments. Pettenkoffer was able to demonstrate from experiments, that, if many persons are in a confined place, it is not carbonic acid alone that causes the very disagreeable sensation of the foul air, but that it is a consequence of the accumulation of harmful products of perspiration through the skin, the particular nature of which has not been determined as yet.
On this account it is permissible to speak of a respiration through the skin, although it has not yet been demonstrated by exact methods that the skin is really absorbing small quantities of oxygen; and it is even now not yet beyond doubt whether the small amount of carbonic acid may not be ascribed, perhaps, to the decomposition of the excretions from the skin, and of the epidermis that is shed, as stated by Prof. Bunge.[233]
But if it is not possible to prove the certainty of respiration through the skin to a degree that would satisfy the postulates of exact science, on the other hand the observations of ancient savants, whose chemical knowledge and powers of observation were not inferior to those of their present successors, in spite of a deficient education in chemistry, all point to its existence, and we shall have to take it into account.
As a rule the various products of skin perspiration cannot be seen, as they are eliminated in the form of vapor. This evaporation takes place in this invisible form, however, only when it is not checked or when it is not produced in excessive quantity. But when such evaporation is hindered by clothing that is impermeable to such products, such as rubber clothes or fur, or when it is too abundant, then it will be eliminated in the form of water through the pores, and will appear in drops. The human body loses from 1 to 1½ liters of this moisture, that is to say, sweat, in a day.
Such checking of evaporation produces a very disagreeable feeling, a fact that indicates the existence of skin respiration; as does also the circumstance that persons clothed in a way that permits of the circulation of air to the skin and the elimination of the products of perspiration, and who also use other means for maintaining a good hygiene of the skin, such as a bath, are always in better health than those who neglect these points.
That the retention of various harmful products normally eliminated through the skin is extremely injurious to health is best shown by the fact that animals whose skin is varnished all over invariably succumb to intoxication. Especially is this true in amphibia, who, as Spallanzani[234] found, can live longer after the removal of the lungs than after varnishing the whole skin. The cause of this is that in amphibia the respiration by the skin is more important than that through the lungs.
But even if, in higher animals, there is far more respiration through the lungs than through the skin, the varnishing over of the skin on the entire body can produce death in certain mammalia. This has also been observed to have occurred in man. The day before the solemn entry into Rome of Pope Leo XIII, a little boy was painted over his entire body with gold leaf so as to represent an angel; but he suddenly died before the procession began. We cannot, however, conceal the fact that the death of higher animals, according to some authorities, is not due to the retention of the products of perspiration, but rather to an increased loss of warmth of the body, especially as these animals have always been shaved prior to being varnished.
Still, for reasons we shall give later, we believe that this cannot alter our views on the harmfulness of checking respiration through the skin. The injurious action of this is also shown by the fact that persons whose skin is burnt to a large extent, die, as a rule, by intoxication. Certain opinions have been advanced which ascribe such a death to a change in the constitution of the blood after extensive burns. I am inclined to think that death may be due to the fact that the skin respiration is, in such a case, more suppressed, as the body is enveloped in bandages which, like sticking plaster, do not admit of air circulation; and also because there is no elimination. At the same time the other parts of the body are covered by the clothing instead of the same being removed. If, however, after such burns the body be kept quite naked and the air thus permitted a free circulation on all sides, then even after the most extensive burns death will not follow, as we have seen in several cases so treated by Dr. Sneve in St. Paul, Minn., whose wards we inspected some years ago. Why should the changes in the blood not induce death in these patients in the same way as it does in patients swathed in bandages? Logically, this cannot be the reason for death, but in all probability it is the suppression of the skin respiration. But if death after extensive burns is due to this cause, then the same may be given as the cause of death after varnishing the body. The substances which are eliminated from the body through perspiration are urea, uric acid (in small quantities only), common salt, creatin, acetic acid, lactic acid, and a number of fatty acids. Although exact science does not demonstrate that poisonous matters are eliminated through perspiration, still some very noted men, like Ortner and Goldscheider, are convinced of it. Arloing contends that the perspiration of even a healthy man is toxic, whereas Queirolo admits this to be so only in the case of sick persons.
We shall also be able to realize the great importance of the skin as an eliminating organ for toxic products after a little consideration on the origin of skin diseases, which we believe are due to two principal causes: Firstly, the invasion of microbes into the skin after a diminution of its resistance, which, in turn, is dependent upon the condition of its nutrition by the blood. This is the external cause. Secondly, by the elimination of toxic products which are formed in the body and then pass through the skin. These may have originally been introduced from the outside, either by food or by drugs, or they may have been produced in the body through products arising from certain glands, such as the thyroid, sexual glands, etc. The waste products of metabolism, such as uric acid, may also be included in this category. This is the internal cause of skin diseases. Both of these causes may stand in relationship; thus the existence of the second may favor the development of the first.
For the subject now under consideration the second cause is more important, and we will say a few words on the matter as showing the importance of the skin as an eliminating organ for toxic products.
We may frequently see persons who are affected by eruptions on the skin after eating certain kinds of food, as oysters or strawberries; and especially after eating oysters which have not been absolutely fresh. In our own case, and in many others which we have observed, an eruption of acne on the face has followed the eating of cheese. A similar state of things may result from taking certain drugs; thus, after bromine or iodine very often acne may be observed on the face. This interesting fact we have experienced personally and have noted in patients who have taken thyroid tablets in certain quantities, which also contain iodine.
If we examine acne eruptions we find in them certain microbes, such as the bacillus of Unna, etc. In gout, which is caused by the retention of uric acid, skin diseases are very frequent.
Sufferers from Graves’s disease, in which there is, as has been so often mentioned, a hyperactivity of the thyroid gland, have very frequently cutaneous eruptions, including acne, and often also a very irritating pruritus. Also in diabetes, in which thyroid hyperactivity plays a prominent rôle, it is not so much the sugar as the factor I have referred to, which is the cause of the great frequency of skin diseases. Here also a number of toxic products are eliminated through the skin.
In women, during menstruation, we often see cutaneous eruptions, as acne or hives. The former is often very distressing in boys and girls in the years of puberty, and it is quite impossible to deny that this may be a symptom of a hyperactivity of the sexual glands. Thus, we often observe acne in persons who are masturbating, or who for a long time live in complete sexual abstinence, so that in certain places the laity term these “pimples of chastity.” Here, again, married life is the best cure for this disease, as it is for so many others.
It is very interesting to note during the question we are now discussing that persons suffering from psoriasis feel relief from their affection when they have had a good opening of the bowels, or when they perspire freely; hence in hot summer weather they suffer less inconvenience than in the winter; also by following a certain diet this disease may be favorably influenced; that is to say, such persons have fewer psoriatic patches when the toxic products are eliminated by the intestines or kidneys. When there is a hyperactivity of the skin function, as in perspiration, the toxic products are eliminated in the vapor or moisture of the perspiration, but during a diminution of this function they form the psoriatic patches.
When the skin function is increased, as in sweating, a number of products that are otherwise eliminated through the urine pass through the skin, which may eliminate a considerable part of the solid waste products, and particularly a very important chemical product—common salt. When the kidney is diseased the elimination of common salt and other substances may become difficult, and thus still more injure the kidneys; these products, and especially the common salt, will be retained. Then comes the skin to the assistance of the kidneys. Not an inconsiderable part of these substances may then pass through the skin when it is in a condition of increased activity, in the form of sweat. Thus the kidneys and skin work in harmony; they are companions, and may be graphically called “Kidney and Co.,” the skin being the second partner. The skin is thus one of our most important organs, and in the following chapter we will deal with its hygiene.