Thyroid deficients, however, are definitely the opposite. They are quite conscious of the limited reserve of energy at their command. Also that they need plenty of refreshing sleep. Early to bed and late to rise remains the leading maxim of health for them. In addition they find it necessary to sleep during the day. Forty winks or more in the afternoon makes a good deal of difference to them. Taciturn, inarticulate, lazy, slow, tired, are the adjectives applied to them by their friends as well as by their enemies. All because of an insufficient or inefficient supply of the thyroid's iodine to their cells. The mobility of energy in an organism is a measure of the amount of active iodine in it. The physiologic synonyms for "energetic and lazy" are "well-iodinized" and "poorly iodinized."
Sensitivity, the ability to discriminate between grades of sensation or acuteness of perception is another thyroid quality. Just as the thyroid plus is more energetic, so is he more sensitive. He feels things more, he feels pain more readily, because he arrives more quickly at the stage when the stimulus damages his nerve apparatus. The electric conductivity of his skin is greater, sometimes a hundred times greater, than the average. Conversely the thyroid deficient type has a low discriminative faculty. Galton has recorded that idiots hardly distinguish between heat and cold and that their sense of pain is so obtuse that some of the more idiotic seem hardly to know what it is. Cretins may moan but never shed tears.
Energy and sensitivity in an individual should direct attention to the thyroid element predominating in his composition. Lack of energy and insensitivity to the degree of thyroid insufficiency in their make-up.
MEMORY, JUDGMENT, AND POISE
In between sensitivity and energy, the sensation and the reaction, comes a passage of the stimulus through the gauntlet of the stored past experience of the individual known as memory. Many hypotheses have been advanced by philosophers, psychologists and physiologists to explain the phenomenona of memory. To conceive of memory materially at all one must admit some sort of memory trace as the basis for the persistence of memory. This memory deposit facilitates the occurrence of the chemical reaction constituting the memory along the same path the next time. Forgetting then consists in a disappearance of these memory traces or deposits. Forgetting is greatest in the first hour after remembering, more than half of the memory trace being lost in that time. Comparison of the curve of forgetting, and the curve of diffusion of a colloid like gelatine from its solution, into a surrounding medium, shows them to be exceedingly similar. Forgetting may be explained by some such loss of the memory trace or deposit into the blood continually flowing by it.
The internal secretions influence the amount and duration of the memory deposits. The thyroid appears to be essential to the laying down of the memory trace. Cretins have poor memories on the retention side and so cannot learn. The memory of thyroid insufficients is wretched. In the extreme grades, the memory for recent occurrences becomes completely lost. Iodine and thyroid increase the electric conductivity of the brain, so that the memory trace must be deposited more easily in those who have an excess of thyroid. Removal of the thyroid produces a degeneration of nerve cells and their processes, and associative memory becomes difficult or impossible because conduction from cell to cell is interfered with. If sufficient thyroid is fed in excess, brain conduction may be so facilitated that epilepsy may result upon slight irritation.
On the other hand, the pituitary seems to be related to preservation of the memory deposit. In conditions of disease of the pituitary, loss of memory for past experiences is more marked. As regards recent experiences, they are better held, although in a sort of subconscious manner, recoverable when the condition improves or is cured. But the greatest difference between the thyroid and pituitary effects upon memory exists as regards material: the thyroid memory applies particularly to perception and percepts, the pituitary to conception (reading, studying, thinking) and concepts.
Judgment is another mental process that often intervenes between sensation and the energy-reaction. It involves memory and association of experiences. Behind it is an attitude as much as there is in an emotion or the arousing of an instinct. Beliefs and reasonings are complex judgments. They form the units of the intellectual process.
There is an element of speed in judgment on reasoning as in perception and memory. And as in the latter, the thyroid determines the velocity. Quick thinking, as we call it, means good thyroid action, and slow thinking deficient thyroid action. The other element in judgment, accuracy, is influenced by the ante-pituitary. During adolescence there is physical growth which consumes most of the secretion of the ante-pituitary. After adolescence, after the early twenties, when physical growth has ceased, the ante-pituitary secretion sensitizes the cells of the brain to mental growth. The reaction potential of the ante-pituitary, that is its inherent, latent ability to supply a maximum of its endocrine for the nerve cells of the frontal lobes, is the best-known chemical determinant of intellectual genius. It makes for the greatest co-ordination of experience, knowledge, information, tastes and problems into one harmonious whole. And curiously, not only does it cause a fusion of intellectual material: it creates a desire for and a love of such material.
We should expect to find extraordinarily well-developed ante-pituitary action among eminent philosophers and men of science, and we do. Adequate action of it is present throughout the range of normals who evidence sufficiently ripened judgment as they progress through life. The ability to profit by experience, and to make more and more accurate judgments as one grows older implies at least a maximum efficiency of it. This maturation is not at all universal. Even after middle age, after forty and fifty years of reasoning, some individuals retain the juvenile mind of their youth. Like the Bourbons, they have learned nothing and forgotten nothing. Their ante-pituitary insufficiency often coupled with a post-pituitary excess, and other instabilities and disequilibriums in the endocrine system, render them immature morons, compared with what might be expected of them for their years. They are the people who are old enough to know better. For the same reasons, inhibition and emotional control are poor in them.