reported in which a uterus was also placed in such an animal, with a means of entry, and pregnancy followed.  If in the castrated female a testicle is planted, the masculine traits become much more marked and striking.  A direct exchange of the male and female roles can thus be achieved.  Castration after puberty cannot modify profoundly structures like the skeleton which are already completed.  Yet it may unquestionably bring about definite retrogressive changes in the secondary sex characters:  reduction or loss of virility, diminution of facial and body hair, and a general presenility or hastening of senility.

How remarkably these interstitial cells influence the entire structure and vitality of the organism is indicated by these facts.  How much they have to do with sexual impulses, sexual excitement, and sexual desire, what the Freudians have popularized as the libido, and how subtly they act upon the coming and duration of adolescence and maturity, as well as sexual precocity and peversions, we shall consider in a later chapter.  But it is enough now to remember that these interstitial glands are the primary dictators of the genital sense and flair of the individual.  In any attempt at measurement of men and women, the quality and quantity of the internal secretion of the interstitial cells must be respected as a fundamental consideration.  The womanly woman and the manly man, those ideals of the Victorians, which crumbled before the attack of the Ibsenites, Strindbergians and Shavians in the nineties, but which must be recognized as quite valid biologically, are the masterpieces of these interstitial cells when in their perfection.  They are such solely because of the right concentration in the blood of the substances manufactured not only by these cells, but by all the glands of internal secretion.  For it cannot be repeated and emphasized too often that the interstitial cells of the sex glands are most sensitive to all kinds of other influences, and, in particular, the other internal secretory organs.  They may indeed be watched as an index scale or barometer of the general tone of the whole internal secretion system.  Sex variations offer a variety of clues to variations, disturbances, predominances and abnormalities in all the components of the ductless gland association.

To take a single instance, the development of the long bones is dependent upon the handling of food lime by the body.  Eunuchs and eunuchoids, that is, individuals with insufficient internal secretion of the interstitial cells, have longer bones and more fragile bones than the normal.  Vice versa, those with an excess of the secretion have shorter and thicker bones.  The earlier the onset of menstruation, which means puberty, the shorter the extremities, as the action of the internal secretion of the ovaries closes the story of the growth of the long bones.