This section is from the book "Health", by W. H. Coefield.
The Kidneys are two organs situated in the abdomen, one on each. side of the vertebral column; their shape is well known, and needs no description. These organs are true glands ; each has a duct which indirectly communicates with the external air.
If we cut a kidney across, we find that the duct (which goes by the name of the ureter) is funnel-shaped where it leaves the kidney, and pointing into that funnel-shaped head of the duct, there are some conical masses of kidney substance; they go by the name of the pyramids of the kidney. When these are examined very carefully, it is found that there are an immense number of fine tubes running through them, called the tubules of the kidney, and they open out at the end of these pyramids, and run straight through the interior substance of the kidney, and then into the outer part of the kidney, where they twist about a great deal. These tubules, when examined under a microscope, are found to end in little bags or capsules. The interior of these bags or capsules is in indirect communication with the external air, because from these little capsules the tubules of the kidneys start, and ultimately open, on the surface of the pyramids, into the funnel-shaped beginning of the ureter-the tube which leaves the kidneys and which is indirectly connected with the external air. Now, an artery comes to each kidney-we will call it the kidney artery;-it subdivides into small branches; these small branches go through the substance of the kidney until they come to the outer part of it, and then they end in very small branches, which go straight into the capsules just mentioned; each small branch of the artery goes into one of the capsules, and immediately breaks up into a bunch of capillaries, forming a little ball in the interior of that capsule, and that little ball, as it were, pushes the lining membrane of the capsule before it, so that between that little ball of capillaries and the interior of the tubule connected with the capsule there is nothing but that very fine lining membrane. Then the capillaries in that little ball run together, forming a small vein that goes out from the capsule. These small veins do not join together to form the vein that leaves the kidney; they do like the portal vein-they break up into capillary vessels surrounding the tubule; these capillary vessels then join together and form a little vein, and then numbers of these little veins join together and form the kidney vein which leaves the kidney.
Now, I want you to see that the kidney is built upon the same theory as the other two excretory organs -the skin and the lungs.
In the kidney, blood is brought by the kidney artery into the little capillary vessels inside the capsules, and so the blood in these capillary vessels is separated from the interior of tubes connected indirectly with the external air merely by a fixve, moist membrane. That is the plan of construction in all these excretory organs; they are all contrivances by means of which blood in the capillary vessels is brought into the nearest possible connection with the external air, brought into connection with tubes connected with the external air, only being separated from the interior of these tubes by a fine moist membrane; and so there are points in all these excretory organs which are similar - the waste substances go through the walls of capillary vessels, and through fine membranes ultimately into the external air. By means, of the kidneys, the following things are got rid of from the blood: in the first place, water, to the extent of about fifty ounces, or two and a half imperial pints, in the twenty-four hours; that water contains certain things in solution: it contains a substance which goes by the name of urea, a waste organic substance, of which I shall have more, to say when speaking about foods; the kidneys get. rid of this substance to the extent of 500 grains in the twenty-four hours, and of another organic body called uric acid, in much smaller quantity: besides this, there are mineral salts, such as common salt, and carbonate and phosphate of lime, and a good many other salts of, perhaps, less importance; so that you see we get rid of the same substances from the kidneys as from the lungs, and skin-water, carbonic acid in the form of carbonate, and organic matter in very large quantities, and also large quantities, of mineral salts.
The quantities I have mentioned are the average amounts excreted by the kidneys of an adult in twenty-four hours.
One more thing we have to consider, and that is how this contrivance acts. The blood is brought by the kidney artery into the ball of capillaries, and the surplus water of the blood, with certain substances in solution, exudes from these capillaries and passes through the fine membrane (just as it would through a piece of filtering paper) into the tubule. Other matters are excreted through the capillaries which surround the tubule, and are then washed away by the watery excretion coining from the capsule.
A few words about the general changes that go on , in the blood. The blood, you see, is being continually renewed from the nutritious parts of the food, partly by absorption from the walls of the small intestines directly into the capillary blood-vessels of the villi, and partly indirectly by absorption from the walls of the small intestines into the lacteal vessels, which, by means of the thoracic duct, convey their fluid into, the blood.
It is renewed with nutritious substances from the food; the white corpuscles, from which we know the red ones are ultimately formed, are continually being formed in the lymphatic glands, and in the spleen, and a few other so-called ductless glands, and perhaps in the liver; these white corpuscles are being continually made, and being added to the venous blood.
To this blood is also added the blood that has been purified in the way I have described in the kidneys, and all this mixture goes to the right side of the heart, is then pumped through the lungs, undergoes the alteration I have described there, especially loses carbonic acid and gains oxygen, then goes to the left side of the heart, and is pumped all over the body into the capillary vessels in the tissues; certain portions of the blood exude from the capillary vessels into the tissues; each tissue takes out what it requires for itself, and leaves the remainder, and, besides that, adds to the remainder the decayed portions of itself.
Whatever blood is not taken up by each tissue goes on into the veins, and to that is also added a certain quantity of the waste substance that comes through the capillary walls from the tissues into the blood; the remainder, viz., the fluid that was not required by the tissues, and some of the waste parts of the tissues, are taken up by the lymphatic vessels, and are conveyed by them into the thoracic duct, and so into the blood again.
While all this is going on, the oxygen gas that has been absorbed into the blood through the lungs is combining, especially in the capillary vessels in the different tissues, with the substances in the blood which are capable of combining with it; and it is combining notably with certain waste substances that the tissues have added to the blood; and I have told you that this combination is attended with the production of heat (all chemical combinations are attended with the production of heat), and this is the way in which the warmth of our bodies is kept up. It is by the conversion of this animal heat, as we call it, into various forces, that we are able to move about, to think, and to do all the various acts that we perform. This combination of the oxygen of the air with substances in the blood produces the waste substances that we get rid of by the organs I have been speaking about,-by means, then, of the combination of oxygen with certain substances in the blood, heat is produced, and the waste parts of the tissues of the body are converted into substances which can be separated from the blood and from the body by means of the organs just described.
Now, a word on the importance of the regular and proper action of these excretory organs, and of the .intestinal canal The former separate substances from the blood that are hurtful if they are kept in the blood. The waste substances that are got rid of by the intestinal canal include the parts of the food that are not digested, and certain secretions from the intestinal canal, especially from the large part of the intestine. These substances are injurious if left in the body, as certain portions of them are reabsorbed into the blood, especially the foul organic matter in them, so that if these various excretory organs do not perform their functions in a proper manner, waste substances are either not separated from the blood or are reabsorbed into it, and poison it, and as the blood is distributed to the various tissues of the body they are not properly nourished, and they become degenerated, weak, and incapable of performing their proper functions; so that the regular action of these excretory organs of the body is of the greatest importance with regard to health, for not a single tissue of the body can be kept in a proper condition if the waste substances are not got rid of in the manner they should be.