230 LOEB— THE CYCLIC CHANGES IN [April 22, 



that has ruptured at the time of ovulation does not degenerate in a 

 similar manner as the other follicles do after they have reached full 

 size, but they grow in a remarkable manner and form a new gland- 

 like organ, the corpora lutea. Now these corpora lutea also degen- 

 erate after a period of growth that lasts approximately seventeen to 

 twenty days. In the corpora lutea resides the mechanism that pre- 

 vents a new ovulation. It is necessary that they degenerate before 

 a new rupture of follicles can take place. As long as they function 

 they prevent ovulation. The fact that the corpora lutea degenerate 

 when seventeen to twenty days old, explains why a new ovulation 

 takes place approximately every three weeks. If we excise the cor- 

 pora lutea at an early date after ovulation, a new ovulation occurs 

 very soon after mature follicles have made their appearance, approxi- 

 mately thirteen to fifteen days after the preceding ovulation. Under 

 these conditions, the normal sexual cycle is reestablished. 



During pregnancy the life of the corpus luteum is prolonged in 

 consequence of the changes occurring in the uterus or developing 

 embryo during the period of gestation and in consequence of the pro- 

 longed life of the corpus luteum, a new ovulation is prevented during 

 the whole course of pregnancy. Toward the latter part of preg- 

 nancy, the corpora lutea again degenerate and directly after com- 

 pleted labor a new ovulation can take place. 



Ovulation, therefore, depends upon three factors : First, upon the 

 maturation of ovarian follicles ; secondly, upon the time of degenera- 

 tion of the corpora lutea ; and. thirdly, upon less important, more or 

 less accidental conditions, as for instance, the process of copulation. 

 The third class of conditions accelerates in many (not in all) cases 

 ovulation, but it is not necessary for its occurrence. Even without 

 a preceding copulation, ovulation usually takes place, but in many 

 cases at a later date. Through what mechanism does the life of 

 the corpus luteum influence ovulation ? It might be conceivable that 

 the corpus luteum delays the maturation of follicles thus preventing 

 a rupture. My observations have, however, shown that an inhibiting 

 influence of the corpus luteum upon the maturation of follicles does 

 not exist. Mature follicles appear frequently during the life of the 

 corpus kitcuni, and especially during the period of pregnancy ; it 



