THE FUNCTION OF THE ENDOCRIN GLANDS
It is these ductless glands, or endocrin glands, or glands of internal secretion (they are known by any one of these names) which especially concern us when we speak of the effect of glands on personality. Besides the ovaries and testes, which give off an internal as well as an external secretion, they include the thyroid and parathyroid glands of the neck, the thymus gland in the chest, the adrenal glands situated just above the kidneys, and the pineal and pituitary bodies both located within the cranium close to the brain.
Because these organs have no visible outlets, it was only within comparatively recent times that they were supposed to have any function at all. Or if a purpose was assigned to them, it was usually highly fantastic and without any basis in fact. Thus the thyroids, which can be easily felt at the lower part of the neck on each side of the trachea, were supposed to keep the larynx moist and so produce a dulcet singing voice. But the thyroids, on account of their conspicuous position, are the glands about which we have the fullest information.
Because the secretions of the endocrin glands flow directly into the blood stream and are therefore carried very quickly to all parts of the body, their exact location is of slighter importance than might at first be thought. Because the pineal and pituitary bodies happen to be situated within the skull, they do not necessarily have a peculiar effect upon the brain. In fact, the thyroid in the neck probably is more closely connected with mental development than either of them. And the function of the pineal is more like that of the thymus than it is that of its nearer neighbor, the pituitary.
The thymus and the pineal. Broadly speaking, we may say that the thymus and the pineal are the glands which control childhood. Both are present and well developed at birth but continue to grow and expand for some years later. Each ceases to grow at puberty when the sexual glands become active. In normal individuals the pineal body disappears entirely after adolescence and very little is left of the thymus subsequent to this period.
The internal secretion of the reproductive glands. Simultaneously with the atrophy of the thymus and the pineal body, the internal secretion of the reproductive glands, which up to this time have been dormant, commences and puberty sets in. The chief effect of the endocrin activity of the testes and ovaries lies in the development of the secondary sexual characteristics. In this connection the investigations of Steinach are the most authoritative as well as the most widely known. His experiments proved conclusively that it is not the reproductive elements proper but the interstitial cells of Leydig, which lie within the larger sex glands, which furnish the internal secretion. Professor Howell sums up Steinach’s primary investigations as follows:
“Making use of very young animals (Steinach) has transplanted the testes from their normal position to other regions. Such animals develop normally, show all of the usual secondary sexual characteristics, and manifest full sexual desire and potency at the proper period. When the transplanted glands are examined the sexual elements are lacking, but the interstitial cells are increased in amount. It would appear from this work that sexual puberty is dependent upon the internal secretion furnished by these cells, and Steinach proposes to designate them collectively as the ‘puberty glands.’ This observer reports further remarkable experiments in which young males (rats, guinea pigs) were first castrated and then had transplanted under the skin or in the peritoneal cavity the ovary from a female of the same species. Under such conditions the graft of the ovary takes, and unlike the grafted testicle both the reproductive cells and the interstitial cells survive. In such animals the secondary male characteristics do not develop, his genital organs remain infantile; he exhibits, on the contrary, the female characteristics, as shown by his size, the character of the hair, and especially by the development of mammae and nipples. So far as the external characteristics are concerned the animal is completely feminized, and Steinach states that such an animal is sought by the male as though it were a true female.”
Working with very old animals, Steinach has further proved that by splitting the seminal duct, thus blocking the external secretion of the testes, the interstitial cells can be made to function more vigorously and a temporary rejuvenation, a sort of second adolescence, can be produced.
Not all of the phenomena usually associated with puberty are, however, caused directly by the activity of the reproductive endocrin glands. Many of them are effected by the interstitial secretions stimulating to greater activity other ductless glands, namely, the pituitary, the adrenals and the thyroid.
The thyroids and parathyroids. So tightly are the parathyroids imbedded in the thyroids in all carnivorous and omnivorous animals, that many fatal operations were performed before it was discovered that the two are separate, if not completely independent organs. Goiters, which are always either enlargements of the thyroids, themselves, or of the connecting tissue surrounding the thyroids, can be easily eliminated by making a small incision in the neck and cutting away the superfluous tissue. In certain geographical regions where the soil contains very little iodine (the most important element in thyroid secretion) the thyroids, in an attempt to overcome this deficiency, grow abnormally large and endemic goiters result. In the country surrounding the Great Lakes of America and in the valleys of Switzerland such goiters are common. Often they are not large enough to be especially dangerous or conspicuous, but in some individuals they attain an enormous size and, of course, their possessors are anxious to have them reduce. Soon after the introduction of medical surgery, many beautiful Swiss ladies went into Paris to have their unbecoming tumors removed. And about half of those who were operated upon died within a few days. The rest recovered and showed no ill effects of their experience. Physicians were at a loss to account for the fatalities. But as animal experimentation was making headway, an explanation was soon forthcoming from the physiological laboratories.
The laboratory investigators discovered that if both thyroids were removed from carnivorous animals the subjects were within a few hours seized by severe convulsions and soon died. Herbivorous animals, on the other hand, lived for a long time after complete thyroidectomy, although they exhibited profound changes in what might be termed their personalities. Anatomical examinations showed that in all carnivorous and omnivorous animals the four tiny parathyroids are imbedded in the thyroid, while in herbivorous species two of the parathyroids are separated from and lie outside of the larger gland. From this it was decided that the thyroids, although they are most important to proper development, are not essential to life, while the parathyroids, through the cancelling effect they have upon various poisons continually given off by the body, are. In the case of the unfortunate Swiss beauties, the parathyroids had been inadvertently cut away with parts of the thyroids in those who succumbed to the operation, but were left intact in those who survived.
The function of the thyroid. The thyroid is the endocrin gland about whose function we have the most complete information. Diseases of the thyroid, in particular goiters, are far from uncommon and the effects of these diseases have been carefully studied. Also the chemical constituents of the thyroid secretion has been determined and an artificial thyroid extract is now easily manufactured. This has been widely used in animal experimentation and as a human therapeutic. In normal individuals the thyroid glands function throughout life. In children they are necessary both to normal physical growth and to proper mental development. In adult life they are essential to body metabolism and mental stability.
The pituitary and the adrenals. Although the adrenal and the pituitary is each a single gland, both of them have two well defined parts. As in the case of the parathyroids and the thyroids, the anterior lobe of the pituitary and the cortex of the adrenals are essential to life, while the medulla of the adrenals and the posterior lobe of the pituitary furnish the secretions which have the more pronounced effect on the personality. Unlike the parathyroid, however, the life-essential portions of each of these glands is intimately connected with sexual development.
The chemical properties of the secretion produced by the medulla of the adrenal glands are known and form the basis of the drug called adrenalin. The effects of this drug have, of course, been carefully studied. The two most important results of an artificial injection of adrenalin lie in a strong stimulation of the nerves which control the heart, the blood vessels and the muscles; and an increase in the amount of sugar in the blood. Translated into more general terms, which will be explained in detail later, this means that the adrenals regulate our emotions as the thyroids do our mental life. And the posterior lobe of the pituitary body, in much the same manner, controls the muscles and skeletal bones directly.
From this brief outline of the role of the various ductless glands it should be evident that a well balanced person, a thoroughly normal individual, is one whose endocrin system is nicely attuned. His every gland secretes just enough but not too much. From the interstitial cells of his sexual glands he gets his secondary sexual characteristics, which until he reaches adolescence were kept in abeyance by his thymus and his pineal. His thyroid keeps his brain active; his pituitary body his muscles well toned; his adrenals his circulation well regulated and his emotional apparatus ready for emergencies. But, let us see what happens to an individual when one particular gland is either more or less active than it properly should be.