It is when a gland, either in the course of development, or because of the influence of starvation, shock, injury, poisoning or infection, begins to undersecrete or oversecrete that its effects upon growth and nutrition become grossly manifest.  A veritable transfiguration of the individual may occur, the black magic of which may perplex him for a lifetime.  A man, made eunuchoid by an accident or by mumps, will observe in himself astonishing changes in his constitutional make-up, mentality and sexuality.  He would be more astounded to learn that beneath the appearances, the changes, so alarming him, there are profound alterations in the rate at which he is taking in oxygen, burning up sugar, accumulating carbon dioxide and excreting waste byproducts through the kidneys, which are responsible for them.

The differences between the normal and abnormal are only a matter of degree.  And so, to be sure, are differences between types.  But it is hard to realize that the striking distinctions between the thyroid type and the pituitary, comparable, as said, to the differences between a greyhound and a bull-dog, are dependent solely upon quantitative variations in the general and local speeds of metabolism, among the cells.

DIVISION OF LABOR

Besides the antagonisms and co-operations between them, there are certain lines along which the glands, in their effects, specialize.  The thyroid, for instance, is concerned specially with the regulation of the shape, form and finish of an organ.  The pituitary shines at the periods of developmental crises, determining them and modifying them.  It exerts the greatest influence upon the time of eruption of the teeth, both the temporary and the permanent, the onset of puberty, the recurrence of menstruation in women, and the time of occurrence of labor.  The interstitial glands distribute the basis of the powers and limitations of masculinity and femininity.  Abnormalities of these glands also affect the individual all along the line, in all of his aspects.  So affected he may apparently change into a wholly different being.  He may change in size, in the shape of his head, feet and hands, as well as in his habits, aptitudes and dispositions.  So he may find it necessary to purchase an entirely different size of hat, more commodious clothes, and newly fitting gloves and shoes.  At the same time, his family, relatives and friends, discover that the erstwhile generous, frank, neat and punctual and liked, has become stingy and suspicious and slovenly and hated.  And all because a gland has begun to undersecrete or to oversecrete.  The transformation will be slight or marked, depending entirely upon the extent of impairment, positive or negative, of the gland involved.

But it is not only in the shaping of the normal individual’s architecture that the internal secretions dominate.  Over that subtle something known in all languages as vitality, expressive of the intensity of feeling, thought and reactions in cells, they rule supreme.  Gay vivacity and grim determination, the temperament of a Louis XIV, and the soul of a Cromwell, are the crystallizations of these chemical substances acting upon the brain.