DIOESTROUS CYCLE IN THE GUINEA-PIG 255 



authors publish, show that corpora lutea formed after the rup- 

 ture of the folhcles, and they state that the folhcles artificially 

 ruptured changed ''into structures almost identical with normal 

 corpora lutea" — except that development was not sufficient to 

 fill the central cavity. 



In the first two animals, which were their best experiments, 

 since the time of the expected 'heat period' was fairly accurately 

 known, the 'heat' came on about the time, or perhaps a little 

 later, than it was expected and was not greatly influenced by the 

 operation. This is just what we should expect on our supposi- 

 tion of the function of the corpora lutea. The dog is a mon- 

 oestrous animal with a long anoestrous period and the destruc- 

 tion of Graafian follicles a few weeks before the oestrus was 

 expected would have no bearing on the probable function of the 

 corpora lutea in bringing on this period. The old corpora lutea 

 resulting from the last ovulation were not disturbed and were 

 probably just about degenerating and thus permitted the oestrus 

 to occur very near the normal time. While the newly formed 

 corpora lutea resulting from the operation were not sufficiently 

 vigorous in their action to do more than slightly delay the 

 menstruation. 



Marshall and Runciman concluded that it is evident that the 

 occurrence of 'heat' in the dog is not dependent upon corpora 

 lutea, and that "The ovarian interstitial cells are possibly con- 

 erned in the process, but cyclical changes in the condition of 

 these cells have not so far been observed in the dog's ovaries." 



These conclusions and Marshall and Runciman's discussion 

 are directed chiefly against Fraenkel's idea regarding the way in 

 which the corpora lutea act; that is, the corpora lutea by their 

 secretion perform an active function in bringing on the oestrous 

 condition. We also disagree on the basis of the evidence fur- 

 nished by the guinea-pigs with Fraenkel's views and for these 

 animals at least such opinions are entirely incorrect. It seems 

 to us, however, that Marshall and Runciman's experiments do 

 not in any way argue against the position that the corpora lutea 

 exert a protective influence over the uterine mucosa, nor that 

 the absence or degeneration of the corpora lutea and the dis- 



