344 THE INTERNAL ENVIRONMENT OF THE BODY Part III 



substances as the female hormones, estrogen and progesterone. This is another 

 aspect of the similarity of maleness and femaleness already mentioned and one 

 of the many cases of the likeness of substances that are active in carrying on 

 different functions. Since every human being inherits traits from a male and a 

 female parent, it is not surprising that the male hormone, androgen, figures in 

 the metabolism of women as well as men and that the female hormone, estro- 

 gen, is in men as well as women. Both hormones appear in the urine of both 

 sexes. Male hormones administered to animals will counteract the effects 

 of the removal of the testes; a castrated male treated with androgen becomes 

 normal except that it has no sperm cells and is of course infertile. 



Castration and Sterilization. Castration of boys and men has been per- 

 formed for various reasons from ancient times into the present. In the past it 

 was done to produce the eunuchs (Fig. 18.9) who served in courts and harems 

 and, as late as 1870, to preserve the soprano quality of voice in boy choristers. 

 By true castration the testes are removed, thus sterilizing the animal; steriliza- 

 tion may also be produced by cutting or tying the duct (vas deferens) from 

 each testis, thus blocking the passage of the sperm cells which are eventually 

 absorbed. This type of sterilization is sometimes used to prevent the breeding 

 of mental defectives and, with the consent of the person involved, for other 

 reasons. 



Female 



Structure and Function. The female reproductive system of mammals is 

 more complicated than that of the male since it not only produces and provides 

 for the eggs, but gives protection and nourishment to the developing young. 

 The structures that take part in this double program are the ovaries, the ovi- 

 ducts (Fallopian tubes), the uterus, vagina and external genitalia, and the 

 mammary glands (Fig. 18.10). Like the testes, the ovaries also produce inter- 

 nal secretions. 



The ovaries develop and remain in the body cavity a little below the kid- 

 neys. Unlike the testes they do not suffer from the high temperature within 

 the body. In mature women, they are the size of a shelled almond, about one 

 and a half inches long and an inch wide. Each one consists of a central core of 

 connective tissue, blood vessels and nerves, enclosed by a covering, the cortex 

 consisting of cords and nests of epithelial cells. This contains the developing 

 eggs and is covered by a single layer of cells, the germinal epithelium, from 

 which the eggs originate. As they develop, they become surrounded by nutrient 

 (follicular) cells. Each egg with its follicular sac forms an ovarian (or 

 Graafian) follicle (Fig. 18.11). Under the influence of an anterior pituitary 

 hormone (gonadotrophic), the follicle grows and a split develops between its 

 outer and inner layers of cells. Into this space these cells or others near them 

 secrete the liquor folliculi, containing the hormone estrogen that is responsible 



