In view of what has been said of the ante-pituitary as the gland of intellectuality, studies of intellectually gifted people having shown well functioning large pituitaries, and of mental defectives in a certain number of cases a small limited pituitary, it is justifiable to regard the factor of inherent capacity as a function of the ante-pituitary.  The factor of zeal or enthusiasm points to the thyroid.  Markedly enthusiastic types are thyroid dominant types.  Vigor as a third factor, the ability to stand stress and strain of continued effort is dependent upon good adrenal and interstitial cell function.  So we may say that craving and capacity for brain work plus ardor plus perseverance in its pursuit, the triplicate of natural ability, are the reflections in conduct and character of balanced and sufficient ante-pituitary, thyroid, and adrenal-interstitial contributions in the chemical formula of the personality.  In the chapter on historic personages analyzed from the endocrine viewpoint, we shall see that some of the most eminent and illustrious people of history have been pituitary-centered.

MENTAL DEFICIENCY

Natural ability grows in an endocrine soil of a particular kind, perhaps affected by the internal secretions much as natural soil is by fertilizers like phosphates or nitrates.  Increased production follows increased fertilization.  Natural disability must vary similarly with a perversion or improper mixture, deficiency or absence of the hormones that combine in natural ability.

It is assumed as a matter of course that the brain itself is there, which, to carry out our analogy, means that the crude soil or earth is there.  Sufficient quantity and adequate quality of nerve tissue must be regarded as prerequisite.  If the brain has been damaged in any way during development or birth, if it has been smashed up in any way, or if it has failed to evolve the minimum number of healthy nerve cells, the endocrine influence becomes negligible.  It is like attempting to insert a key into a door which has no lock.

It is among the specimens of normality of the brain cells that we may look for our examples of endocrine mental deficiency.  Included are all sorts of examples of feeble-mindedness varying from the moron to the imbecile and idiot, arrested brain life.  The cretin is the classic type of mental deficiency due to endocrine insufficiency, curable or improvable by the proper handling.

Insanity, degeneration of the normal brain life, may be caused by an upset of the endocrine balance.  Among the commonest manifestations of insanity are excitements and depressions, apathies and manias, hallucinations, delusions and obsessions, all of which are reproducible under known conditions of internal secretion excess or failure.  Alternating states of mania and depression are caused in some instances by extreme hyperthyroidism.  The critical periods