CESTROUS CYCLE IN THE GUINEA-PIG. 24! 



nection that each stage in the condition of the uterine wall during 

 the cestrous is of short duration and unless the uterus be removed 

 at a given time, the abundance and position of the leucocytes and 

 the condition of the uterine wall will be changed. Chance was 

 against Loeb's removing the uteri from the non-copulated females 

 at the moment of maximum leucocyte migration, since he had 

 no exact means of knowing when this would occur without 

 having first observed copulation. 



Active migration and accumulation of leucocytes may be 

 observed in the entire absence of sperm fluid. The role of this 

 fluid and the modification of the shedding or slurring off of the 

 vaginal and uterine epithelium in its presence was fully brought 

 out in the discussion above of the vaginal plug. 



Loeb's estimation of the ovulation times and uterine changes 

 from microscopic examination of fixed specimens does not make 

 it possible to know within a few hours, or even days, of the 

 exact moment of ovulation in a given living individual. He 

 states, however, on page 31, that to determine the effects of the 

 removal of the corpora lutea on the duration of the sexual cycle, 

 it "was necessary to determine the length of the cycle in the 

 normal guinea-pig." Not only is this necessary, particularly in 

 view of the wide variations Loeb finds in the normal sexual cycle 

 among different individuals, but it is better or even necessary, 

 to know the actual length and variations of the sexual cycle in 

 the given specimen experimented upon. As evidence of the 

 correctness of the last statement, we may cite Loeb's method 

 and results in determining the normal cycle lengths. This was 

 done "by observing the time of heat of a guinea-pig and by 

 examining the uterus and ovaries at known intervals" (after 

 removal from different individuals). Such examinations were 

 made on many specimens that had to be either killed or operated 

 upon. The following ovulation intervals were thought to be the 

 normal sexual cycles, page 31, "We found the length of the sexual 

 period to be usually sixteen to eighteen or nineteen days; some- 

 times the new ovulation may take place as early as fifteen days 

 after copulation. In two exceptional cases we observed the 

 new ovulation as early as thirteen and a half to fourteen and a 

 half days." The sexual cycle, therefore, varies in length from 



