THE HORMONES IN HUMAN REPRODUCTION 



or records of menstrual cycles, because the animals had been 

 shot in the jungle by hunters. As regards the relation of 

 menstruation to ovulation in the cycle of the monkey, the 

 results of Heape and Van Herwerden were obscure and puz- 

 zling. Heape in his few cases observed no clear relation. Van 

 Herwerden actually found that in some of the Hubrecht 

 specimens the uterus was menstruating but there was no 

 corpus luteum at all in the ovaries. In other menstruating 

 animals a corpus luteum was present. This variability could 

 perhaps be reconciled with the older theories of the human 

 cycle, but not with the Meyer-Schroeder-Fraenkel theory. 

 The absence of life histories, however, cast uncertainty upon 

 the significance of Van Herwerden's observations. A hunter's 

 specimen lets us see only one instant in the life of the animal ; 

 who could tell the significance of these puzzling cases so 

 completely removed from the context of life? 



Meanwhile the German interpretation seemed plausible 

 indeed. It could be matched without difficulty to all the 

 recently gained knowledge of the cycles of mammals. Stock- 

 ard and Papanicolaou's studies of the guinea pig (1917), 

 those of Long and Evans on the rat (1921), which I had 

 been privileged to watch for four years, and my own on 

 the domestic pig had all emphasized the occurrence of regular 

 cycles of ovulation followed by the progestational phase 

 of the uterus. I supposed that application of the same 

 methods to a menstruating mammal, namely the Rhesus 

 monkey, would reveal a strictly parallel sequence, with men- 

 struation as its last stage. If I kept my animals in good con- 

 dition, observed their cycles with perfect vigilance, and 

 autopsied them at carefully chosen stages in their cycles, I 

 should obtain a series confirming the German theory. I 

 thought that 25 monkeys and three years' work would suffice 

 to establish the normal cycle, after which we could go on to 

 all sorts of experimental studies in confidence that we could 



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