THE OESTROUS CYCLE IN THE MOUSE 331 
8. GENERAL DISCUSSION 
The literature on this subject is so extensive that it is practi- 
cable to discuss here only that bearing directly on special phases 
of this work. 
In many particulars the oestrous changes in the mouse are 
similar to those described by investigators of other rodents. 
Important among the recent workers in this field are Heape 
(05), on the rabbit; Konigstein (07), on the rabbit, rat, and 
guinea-pig; Rubaschin (’05), Bouin and Ancel (710), L. Loeb 
(11), Lams (713), Stockard and Papanicolaou (717), on the guinea- 
pig, and Long and Evans (’20), on the rat. 
Many of my observations merely establish for the mouse proc- 
esses previously described in other rodents. It has been a 
pleasure to confirm in many instances the observations of earlier 
investigators, but in some respects conditions in the mouse throw 
a new light on certain of these sexual problems and a few new 
interpretations seem warranted. 
In discussing the duration of the cycle, Heape (00) says: ‘‘The 
differences in sexual periodicity in polyoestrous mammals in 
allied forms and even within the limits of the same species is 
due to variation in the quiescent period.’’ In the mouse another 
possibility presents itself. The mode of the curve for the cycle 
duration in brown mice is six days—an interval of two days 
longer than that for black and white and one day longer than 
that for yellow and gray. Long ‘heat’ periods are more common 
to browns than to the other strains. Therefore, although the 
variation in the dioestrous interval accounts for much of the 
cycle variation, a good deal of it is also due to the variation in 
the duration of the oestrous stage itself. The variation in cycle 
length is great sometimes in the same animal and among dif- 
ferent individuals from one litter. In the latter, however, it is 
less than in different strains of mice. 
As stated earlier in the paper, albinos in our stock are browns 
minus the color factor. The mode of the curve for whites being 
two days shorter than that for browns suggests that with the 
loss of the determiner for color a shorter cycle has been effected. 
Again the modes of the curves of cycle duration of yellow and 
