This section is from the book "Health", by W. H. Coefield.
You see already, from what I have told you, that in the liver certain substances are separated from the blood, and certain substances added to it.
I will go on at once to speak of the important organs which separate the waste substances from the blood; they are called JExcretory Organs, and are the lungs, the skin, and the kidneys. The Lungs I have already described to you, but I want to remind you of this, that the lungs are organs the interior of which is in connection with the external air, organs which are very highly supplied with blood, organs in which the blood is brought into almost immediate contact with the external air, being only separated from it by a fine moist membrane. The lungs separate from the blood, in the first place, waste carbon in the form of carbonic acid. Now carbon, or charcoal, is a substance that is contained in almost all our tissues, and in almost all our foods, so that it is a substance that is being continually added to the body, and has to be continually got rid of. The amount of carbon, in the form of carbonic acid, that is got rid of by the lungs of an adult in twenty-four hours is very nearly eight ounces, or half a pound. Besides carbonic acid, water, on an average about nine ounces, or very nearly half an imperial pint, is got rid of from the lungs of each individual in twenty-four hours, and also a certain amount of foul organic matter.
The other excretory organs-the skin and the kidneys-get rid of these same substances, water, carbonic acid, and organic matter; and the kidneys, in addition, remove large quantities of mineral salts.
The Skin of the body consists of two chief layers. The first, or outer layer, goes by the name of the scarf-skin or epidermis. It is insensible, horny, not supplied with blood, dead, and consists of scales, which are continually falling off. The deeper layer is very largely supplied with blood, running, of course, in capillary vessels, and a certain amount of exudation from that is able to take place through the epidermis or scarf-skin. This is of very small importance, but of much greater importance is the fact that certain substances are separated from the blood in the true skin by means of glands. There is an enormous number of glands situated in the true skin of the body. These glands are true glands. They consist of structures around projections from the surface of the skin, and go by the name of sudoriparous or sweat glands, or perspiration glands.
Each of these glands consists of a long tube that is pushed in from the epidermis, as it were. It starts at the surface or scarf-skin, and runs through in a corkscrew-like fashion into the true skin, and is there twisted up into a ball, which contains a very large number of capillary blood-vessels.
By these sudoriparous or perspiration glands, a fluid is secreted, consisting of water having a very small quantity of salt and organic matter dissolved in it It is found also that by these glands a certain quantity of carbonic acid gas is got rid of from the blood, and that through them a small quantity of oxygen gas gets into the blood, so that you see the action of these glands is similar to the action of the lungs, only that the quantities of the substances got rid of are different From the lungs a large quantity of carbonic acid is got rid of- from the glands a very small quantity; on the other hand, in twenty-four hours, about twice as much water is ordinarily got rid of from the perspiration glands as from the lungs-about eighteen ounces. This amount varies with the temperature, exercise taken, etc.
The number of these glands that are found in the true skin varies very much in different parts of the body, but altogether there are two and a half millions on the surface of the body. The openings of their tubes are commonly known as the pores of the skin.
There are other glands in the true skin which do not perform the functions just described.
Connected with the scarf-skin there are certain structures in different parts of the body which are peculiar varieties of the epidermis or scarf-skin: such are the nails and hairs.
In connection with the hairs there are certain little glands called sebaceous, or, if you like, little glands which secrete an oily fluid, a kind of natural grease for the hair and skin. It keeps the hair and skin constantly lubricated. I may also mention here, that attached to the roots of the hairs in the skin there are small involuntary muscles, the object of which is clearly to move the hairs. They are capable of contracting under certain very strong stimuli, and when we say that a person's hair " stands on end " when he is very much astonished or under strong excitement, it is not a fiction, but literally the fact. Any strong emotion may indirectly cause the muscular fibres to contract, and the hair to stand on end.
From the surface of the skin, just as from the lungs, besides the substances that are got rid of from the blood, heat is lost I told you that a considerable quantity of heat is lost from the lungs, so, too, a considerable quantity is lost from the surface of the skin. Now, this action I have just described of the perspiration glands in the skin is an action of extreme importance, and so it is of the greatest importance that we should keep the surface of our skin continually freed from the secretion of these glands which is being continually poured out The action of these glands is continually going on although we do not notice it Water is continually evaporating from the surface of the skin.
The continual action of these glands goes by the name of insensible perspiration. When we visibly perspire, it is because, from some reason or other, these glands act more than usual, and secrete so much fluid on the surface of the skin that it cannot be got rid of by evaporation as quickly as it is formed. It is of extreme importance, however, that it should not accumulate, and so choke up the pores of the skin, as is commonly and quite rightly said. If this is allowed, then much of the action of the skin in separating waste substances from the blood is thrown upon the other excretory organs-viz., the lungs and the kidneys-and these organs get too much to do, and so become diseased. This is one cause why towards the latter end of life those organs frequently become diseased. You can actually as certainly kill an animal by varnishing his skin over as by cutting his throat.