CESTROUS CYCLE IN THE GUINEA-PIG. 239 



records. This knowledge of the definitely changing structure 

 of the vaginal fluid made it possible to study the cestrous cycles 

 in many living females and reduced the time element of ovulation 

 in the guinea-pig to a certainty. 



We considered in a somewhat different manner the connection 

 between the uterine reaction and the secretion of the corpora 

 lutea, though essentially we share Loeb's ideas of the functions 

 of these bodies. It was concluded that the duties of the corpora 

 lutea are probably about what Beard ('97) long ago argued in his 

 monograph on "The Span of Gestation and the Cause of Birth." 



The development and the degeneration of the vaginal and 

 uterine mucosse were found to follow very closely the development 

 and degeneration of the corpora lutea in the ovaries. The case 

 was stated as follows: 'The breaking of the Graafian follicles 

 occurs during the oestrus as a result of congestion which began 

 in the theca folliculi at about the same time as the congestion 

 of the stroma of the uterus and vagina. And finally when the 

 regenerative growth of the uterine mucosa sets in, the ovaries 

 then possess new corpora lutea in an active state of differentia- 

 tion which have been derived from these recently ruptured 

 follicles." The presence of the new active corpora lutea sup- 

 presses the final steps in the development of the almost mature 

 Graafian follicles in both ovaries, whether the corpora lutea be 

 located in only one of the ovaries or both. When the corpora 

 lutea become less active and their degeneration has proceeded 

 to a certain extent, another ovulation may then take place. 

 Therefore, the functions of the corpora lutea are probably, first, 

 by their presence and activity to inhibit ovulation or to determine 

 its time, and, secondly, to preserve the structure of the uterine 

 wall and prevent its degeneration. 



Loeb has* attacked the problems of corpora lutea function in 

 the guinea-pig in a more direct experimental way than have other 

 investigators. Yet while studying the effects of corpora lutea 

 removal on the length of the ovulation period, he has been 

 handicapped by the fact that his animals, after the initial 

 operation, were later killed for examination and thus were no 

 longer available for a continuation of the experiment. Only 

 one observation was obtained from any particular female. The 



