CAUSE OF HYPERTROPHY OF SURVIVING OVARY 67 



Hatai ('13) also found in the adult semispayed rats that the 

 weight of the surviving ovary is almost twice the weight of the 

 normal single ovary in the control of like age. 



It is clear from the foregoing that both in albino rats and in 

 rabbits the surviving ovary hypertrophies at least within one 

 to five months after operation, and weighs usually twice or more 

 than twice the normal ovary, and it seems also certain that the 

 compensatory hypertrophy is not necessarily dependent on coitus 

 or pregnancy. These statements are based, however, on obser- 

 vations made on adult animals, that is, after puberty, and so 

 far as I am aware, there are no previous observations on the 

 changes in the surviving ovary before puberty. My own obser- 

 vation shows, however, that even before puberty the surviving 

 ovary exhibits a definite amount of hypertrophy within a short 

 time after semispaying, namely, three to five weeks, though its 

 increase is not so large as that found in the surviving ovary of 

 adult animals, since in the prepubertal period, the surviving 

 ovary weighs only about 40 per cent more than the normal ovary 

 of control rats. 



With the exception of the suggestion of Bond, the real cause 

 or causes of the compensatory hypertrophy have not been con- 

 sidered. With the purpose of getting an explanation, therefore, 

 I have compared the total number of ova and of corpora lutea 

 in the normal ovary with those found in the surviving ovary in 

 these eight litters of rats. 



Total number of ova in the surviving ovary compared with total 

 number of ova in the normal control ovary of like age 



In each litter I have counted the number of ova in the left 

 surviving ovary of two semispayed rats and in the corresponding 

 left ovary of one control rat belonging in the same litter and of 

 like age. I have also counted the number of ova in the ovaries 

 removed from the semispayed rats at the age of twenty days, 

 the time of operation. There are altogether eight litters, and 

 thus results have been obtained for the number of ova in sixteen 

 semispayed and eight control rats, as shown in table 5. For 



