THE NATURE OF GLANDS
The human body contains many thousands of glandular structures, some large, some small, some simple, some complex, but all of them absolutely essential to its proper growth and health. Some of these organs which are most familiar are the sweat glands through the skin, the salivary glands of the mouth, the gastric glands of the stomach, the liver, the kidneys, the pancreas, and the male and female reproductive glands. Except for those of reproduction, the glands in this list are not to any especial extent connected with personality. Of course, if they do not function correctly, the health is impaired and changes in temperament result. But that much can be said of any other physiological organ. For the most part these glands of external secretion, as they are called, each has its own specific function to perform. They take up certain substances from the blood stream, or from the intestinal tract, transform them and then emit them through well defined ducts. In this manner the kidneys secret urine, the liver bile, the gastric glands gastric juices. The ducts or tubes which carry the transformed substances to the exterior are essential parts of the glands, themselves, and the secretions are always ejected through them.
There are, however, other glandular structures in the body which have no definite outlets. The substances which they secrete do not pass out through well defined passages but are absorbed directly by the blood stream. Their effect is the same as that of drugs injected into the blood by a hypodermic needle. In fact, if the chemical constituent of a ductless gland’s secretion is known and can be prepared in the laboratory, the same results can be got through its artificial injection as from the increased activity of the gland itself.