144 



Scientific Proceedings (107). 



This variation in the effect of the underfeeding when applied 

 at different periods of the dicestrum is associated with the fact that 

 the conditions of the ovary differ at the different times. 



Shortly after an ovulation the ovary contains almost entirely 

 small primary follicles. These follicles are not so unfavorably 

 affected by food conditions as are the large graafian follicles, 

 which begin their growth and development during later stages of 

 the dicestrum. 



A large follicle at the height of its development seems to require 

 much better nutrition than a small primary follicle, and the lack 

 of proper food arrests its progress very readily. Thus a late 

 underfeeding has a more injurious effect than an early one, and 

 the postponement of the next oestrus is correlated with a post- 

 ponement of the development of new ripe follicles in the ovary. 

 The entire oestrus activity depends chiefly upon the conditions 

 prevailing in the ovary. 



The fact that following a late and long underfeeding the next 

 ovulation is delayed about 11 days after the underfeeding has 

 been stopped is in accord with the results of operation experi- 

 ments which Papanicolaou has performed on the corpora lutea in 

 guinea-pigs. 



These experiments show that after removal of all young corpora 

 lutea following an ovulation, the next ovulation arrives in about 

 11 days instead of 16 to 17 days as would be expected. This 

 acceleration of 5 to 6 days is due to the absence of the corpora 

 lutea, which if present evidently inhibit the maturation, or prolong 

 the time necessary for the development, of ripe follicles in the 

 ovary. 



These experiments all demonstrate the sensitiveness of the 

 follicles within the ovary to environmental conditions and when 

 considered in more detail than is here possible, they throw light 

 on many peculiar reproductive phenomena observed in nature. 

 The extreme variations in the cestrous cycles recently recorded for 

 the rat by Long and Evans (Proc. Am. Ass'n of Anatomists, 

 Anatomical Record, April 1920) may be in part, at least, due to 

 the variations in the diet taken by the individuals. When rats 

 are fed a mixed diet no doubt certain individuals receive a ration 

 quite different from that eaten by certain other members of the 

 olony. 



