rease the capacity for muscular work. Whether this was a direct
effect upon the muscles, or indirect through the nerves or other
endocrines, no one can say. Certainly the carriage of an individual,
outer symptom of the inner tonus among his muscles and tendons, may be
said to be as distinctively an endocrine affair as the color of his
skin. And like its variations, variations of their tone, development,
reactivity, fatigability, and endurance may be traced to corresponding
states of overaction, or underaction, and odd combinations of the
different hormones. Much remains to be learned about them and the
manner of their control. Such an affliction as flatfoot, dependent
upon a laxity of the ligaments in one who seems perfectly healthy and
strong, may lead the analyst back to a thymus-centered personality.
That is but one example.

Since, too, muscle attitudes, muscle tensions and muscle relaxations
play so large a part in the production of fundamental mental states:
the attitudes, moods, memories and will reactions, the vegetative
apparatus enters, to play its part as a determinant.

SEX

Over no domain of the body have the endocrines a more absolute
mandatory than over that of the whole complex of sex. Both as regards
the primary reproductive organs, their size and shape, and the
character of their implantation, malformations and anomalies, as well
as the physical and mental traits lumped as the secondary sexual,
puberty, maturity, and senility, voice changes and erotic trends,
virility and femininity, the internal secretions are dictators at
every step. So significant are these, that even a rough summary of the
discoveries and the outlook in the field involves some consideration
of the details.

CHAPTER VI

THE MECHANICS OF THE MASCULINE AND THE FEMININE

It needs a poet to chant the epic of sex. The mystery of it puzzled
the minds of the earliest Sumerian thinkers. As a source of deepest
excitement, it generated the most revolting ceremonies, bizarre
customs, astounding cruelties and incomprehensible stupidities of
the race. Men and women, as soon as they have done with their usual
business of keeping themselves free of disagreeable sensations,
hunger, cold, fear of enemies, betake themselves to it as a primary
interest all over the world. The most advanced psychologists of the
day link the sex impulse with the windings and twistings of all human
activity.

Yet the Homer of sex through the ages is still