THE HORMONES IN HUMAN REPRODUCTION 



skin. A hypodermic needle of large diameter can be inserted 

 and the pellet pushed through its canal. Once buried, the sur- 

 face of the pellet is slowly dissolved and the hormone is thus 

 received by the animal in very small but continuous dosage. 

 In this way it acts very effectively over long periods of time 

 with the minimum disturbance of the animal. The method is 

 extremely useful in laboratory experiments and there are re- 

 ports of its successful use in certain human cases. There is 

 still much to be learned, however, about the rate of absorption 

 of these pellets, before we can know what daily dose we are 

 actually giving when we administer the hormone in this way. 



What part of the ovary makes the estrogenic hormone? 

 After a great deal of investigation it is generally considered 

 by the experts that the estrogenic hormone is probably made 

 in the walls of the follicles, both large and small. The evidence 

 for this conclusion is indirect, for there is no way to locate 

 the hormone directly. The best we can do is to put little frag- 

 ments, taken from various parts of the ovaries of large ani- 

 mals, under the skin of castrated mice to see if they contain 

 estrogenic potency. Some years ago A. S. Parkes of London 

 astonished his fellow workers by reporting that he had found 

 a way (by use of X-rays) to break down the follicles in the 

 ovaries of mice and thus to reduce the ovaries to masses of 

 nondescript cells. Such mice became sterile, of course, because 

 they could not produce eggs, but they went on having estrous 

 cycles more or less regularly. This teaches us that the ovarian 

 cells which make the estrogenic hormone can do so even when 

 not actually organized into follicles. 



I have already mentioned that during pregnancy the human 

 placenta contains a large amount of estrogenic hormones. We 

 know that these are not made in the ovary but in the placenta 

 itself. There are several cases on record in which the ovaries 

 were removed during pregnancy but the supply of estrogen 

 continued. In humans and animals that are not pregnant the 



{ 92 } 



