THE HORMONES IN HUMAN REPRODUCTION 



ing number of corpora lutea have to be searched for and 

 removed at the operation. 



As already explained on p. 68, rabbits are peculiar in 

 that the ovarian follicles ripen only after mating, not 

 spontaneously at more or less regular intervals, as in other 

 animals. This is a great advantage for the present purpose, 

 for it means that we can time our experiments at will. 

 Fraenkel simply mated his females to buck rabbits of known 

 fertility. He knew they would ovulate next day and that 

 while the eggs were being fertilized and beginning to develop, 

 the ruptured follicles would be transformed into corpora 

 lutea. Sometime during the next 6 days he intervened surgi- 

 cally and destroyed the corpora lutea. Then he simply waited 

 to see what happened. If loss of the corpora did nothing, 

 he could expect that after 3 weeks the rabbit would show 

 signs of pregnancy and about the 33rd day, as is the 

 rule in this species, she would give birth to her litter of 

 young. Actually, when the experiment was performed as 

 described, no pregnancy ensued. Something had interfered 

 with the embryos. Fraenkel checked this result by careful 

 control experiments; he removed only one ovary, or cut 

 into both ovaries without removing the corpora lutea. Thus 

 he had experiments in which there was no endocrine loss, but 

 just as much upset and damage as if the corpora lutea had 

 been removed. The results were decisive. If the corpora lutea 

 were not completely removed, the pregnancy went on. If 

 they were removed, the pregnancy failed. In many cases he 

 did not wait for the time of birth, but autopsied the rabbit 

 3 or 4 weeks after operation, always finding that the embryos 

 had disappeared from the uterus. He did not learn what had 

 actually happened to them, nor when the blow fell. He only 

 knew they could not survive the loss of the corpora lutea. 



These results were presented to the German Gynecological 

 Society in 1903, but they met a good deal of criticism and 

 disbelief. Some of the experiments were for technical reasons 



( 106 } 



