THE HORMONES IN HUMAN REPRODUCTION 



of the race. Certainly our customs would be very different 

 from what they are if the sexual compulsions of women were 

 like those of animals with strongly marked estrous periods. 

 In these creatures the sex response, intense and irresistible 

 in the female during estrus, is wholly absent at other times ; 

 in the human species it is moderated but diffused over a 

 larger proportion of the time. In their various aspects and 

 sublimations, from downright sex desire to affection and 

 vague romantic yearnings, the impulses of sex color in some 

 degree our entire adult lives, teach us to love nature and art, 

 and call us to sacrifice and devotion. In this respect above all 

 mankind differs from the beast. 



Regardless, however, of this all-important difference of 

 behavior, the cycle of the ovary proceeds in the human species 

 as in the others (Fig. 22). The follicle ripens and ruptures, 

 the egg passes to the uterus, the corpus luteum forms and 

 takes up its endocrine function. The lining of the uterus 

 undergoes a profound progestational change. The epithelial 

 cells of its glands multiply so greatly that the glands have 

 to become sinuous and pleated, in order to be accommodated 

 in the available space. The glands fill up with fluid secretion 

 and therefore become dilated. The result is a very character- 

 istic appearance, when seen in sections of the uterus. This 

 progestational or "premenstrual" state is well shown in 

 Plate XXI, C. 



Inspection of the diagram (Fig. 22) will show that the 

 premenstrual phase is at its height during the second week 

 after discharge of the egg from the ovary, just as in other 

 mammals. If there is a mating, and the egg is fertilized and 

 becomes an embryo, it will reach the uterus when the endo- 

 metrium is fully under the influence of the corpus luteum and 

 ready to take care of the new arrival.^ This is clearly illus- 



3 We do not actually know the time of arrival of the human embryo 

 in the uterus, nor the precise time of its implantation, since no normal 



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