Like the pituitary, each adrenal gland is a double gland, that is, consists of two distinct portions, united together, one might say, by the accident of birth. It would be confusing, however, to speak of each as two glands, because there are, as a matter of fact, two separate adrenal glands, one in the right side of the abdomen, and the other in the left. Each gland is composite, or duplex. How the two parts came to be united is a long story, interesting but too long to be recounted here. In fishes they are apart and independent.
Each adrenal is a cocked hat shaped affair, astride the kidneys, easily recognized because of its yellowish fatty color. Indeed, for centuries the glands were not given a separate status as organs, but were passed up as part of the fat ensheathing the kidney. In childhood and youth, in common with the other glands, they are relatively larger and more prominent than in the adult. Also, at every age, the amount of blood passing through them is very large compared to their size. Their tremendous importance in the body economy accounts for their being so favored.
The two parts of which each gland is composed, are known as the cortex or outer portion (literally the bark) and the medulla or inner portion (literally the core). No clean-cut boundary sharply delimits the two, as strands and peninsulas of tissue of one portion penetrate the other. In the history of their development in the species and the individual, and in their chemistry and function, a sharp difference contrasts them.
In the embryo, the cortex is derived from the same patch that gives rise to the sex organs, the ovaries in the female, and the testes in the male, described as the germinal epithelium. How intimately the two sets of glands are connected is neatly pointed by this fact of a common ancestor. All vertebrates possess adrenal glands. In the lowest of the vertebrates, Petromyzon, the two parts are distinct, the cells of the cortex-to-be are situated in the walls of the kidney blood vessels, projecting as peninsulas in the blood stream, the blood sweeping over and past them. The medulla-to-be consists of cells accompanying the vegetative nerves. Among reptiles, the two become adjacent for the first time, and among birds one part occupies the meshes of the other. The size of the cortex varies directly with the sexuality and the pugnacity of the animal. The charging buffalo, for example, owns a strikingly wide adrenal cortex. The fleeing rabbit, on the other hand, is conspicuous for a narrow strip of cortex in its adrenal. Human beings possess a cortex larger than that of any other animal.
No definite chemical substance has as yet been isolated from the cortex. That remains a problem for the investigator of the future. But certain observations, especially concerning the relation between the development and behaviour of the so-called secondary sex characteristics, those qualities of skin, hair and fat distribution, physical configuration and mental attitudes, which distinguish the sexes, and the condition of the gland, indicate clearly that an internal secretion will be isolated, and that it will in its activity furnish certain predictable features.
Three different layers of cells, arranged in strings, that interpenetrate to form a network directly bathed by blood, that breaks in upon them from open blood vessels, compose the cortex. Most remarkable is this method of blood supply for it is exceedingly common among the invertebrates and rare among the vertebrates.
In certain disturbances of these glands, especially when there are tumors, which supply a massive dose of the secretion to the blood presumably, peculiar sex phenomena and general developmental anomalies and irregularities are produced. If the disease be present in the fetus, taking hold before birth, and so brought into the world with the child, there evolves the condition of pseudo-hermaphroditism. The individual, if a female, presents to a greater or less extent the external habits and character of the other sex. So that she is actually taken for a man, although the primary sex organs are ovaries, often not discovered to be such except when examined after an operation or death. How closely such an occurrence touches upon the problems of sex inversion and perversion comes at once to mind.
If the process involving the adrenal cortex attacks it after birth, the symmetrical correspondence and harmony of the primary sex organs and the secondary sex characters are not affected. But there follows a curious hastening of the ripening of body and mind summed up in the word puberty, a precocious puberty, with the most startling effects. A little girl of 2, 3, or 4 years of age perhaps will come to exhibit the growth and appearance of a girl of 14. She begins to menstruate, her breasts swell, she shoots up in height and weight, sprouts the hair distribution of the adult, and the mentality of the adolescent, restless, acquiring, doubting, emerge. A tot bewitched into puberty! A boy of six or seven may suddenly, in the course of a few weeks or months, become a little man, robust, rather short and stocky, but moustached, with the muscular strength and sexual powers of a man and thinking as a man. It is all as if into some fermentable medium or solution a little yeast were dropped that changed the quiet calm of its surface into a bubbling, effervescing revolution. It suggests at once that maturation, the transformation of the child into the man or woman, must be due to the pouring into the blood and the body fluids of some substance which acts like the yeast in the fermentable solution. The adrenal cortex is one source of the maturity-producing internal secretions.
If trouble in the adrenal cortex starts after puberty, phenomena of the same type, but of a different order, exhibit themselves. A woman, say in the thirties, becomes thus afflicted. Slowly or quickly her body will be covered by an abundant growth of hair, more or less of a beard and moustache appear upon the face, her voice will become deep and penetrating, her muscles will harden, and she will show a capacity for hard physical labor. Sexually she appears to be made over, masculinity now predominates in her make-up. Virilism is the name by which the French in particular have popularized the knowledge of the condition. Virilists have to shave or be shaved regularly and are not bothered in the least by the cares, responsibilities, jealousies and anxieties of personal beauty, for the change in their spirituality makes them immune to the preoccupations of the feminine. The cause of such a transformation in a previously entirely normal woman has been found to be a tumor of the adrenal cortex.
But not only is sexuality, and the conduct of the secondary sex characters, connected with the adventures of the adrenal cortex. The development of the master tissues of the body, the brain, the pride and darling of evolution, is in some subtle way correlated with it. The adrenal cortex contains more of the phosphorus-containing substances of the general nature of those found in the central nervous system than any other gland or non-nervous tissues in the body. During human intrauterine life the adrenal glands are large and conspicuous, in the first half of the second month being twice as large as the kidneys. Most of this relatively huge size, which happens in the human alone, and not in other animals, is due to enlargement of the cortex. Should this preponderance of the cortex over the medullary portion not occur in the human, that is, if the proportions remain like those of other animals, the brain fails to develop properly, or an entirely brainless monster is generated. The human brain, therefore, probably owes its superiority over the animal brain, to the adrenal cortex, in development anyhow. The growth of the brain cells, their number and complexity is thus controlled by the adrenal cortex.