FERTILITY 99 



of the generative organs is characteristic of the spring 

 season. At this season most animals, domestic and wild, 

 are periodically in heat. This greater activity is un- 

 doubtedly due to the abundant supply of nutritious and 

 succulent grass. That this kind of food does materially 

 influence the fertility of animals is recognized by the 

 shepherds of England in the practice of flushing ewes. 

 This practice consists in turning the ewe flock on rich 

 succulent pastures about two weeks before turning in 

 the ram. The flock owners believe that this increases 

 the number of lambs and brings the ewes more uniformly 

 in heat. The Beinn Bhreagh x flock of sheep in Nova 

 Scotia belonging to Dr. Bell when fed generously before 

 and during the mating season produced a larger number 

 of twins. The older ewes also produced a larger per- 

 centage of twins. 



97. Excessive food supply and nutrition. An over- 

 supply of nutritious food which causes the animal to 

 become abnormally fat is often the cause of sterility 

 among the domestic animals. In nature it is rare for 

 an animal to remain continuously in an excessively fat 

 condition. At certain seasons of abundant food supply 

 the wild animal may become fat, but such periods of 

 plethora are invariably followed by a scarcity of food, 

 and such food must often be gathered by exhaustive 

 exercise. Such variations, if not extreme, may be partic- 

 ularly favorable for the functioning of the reproductive 

 system. Certain it is that the most skillful stockmen 

 have long recognized the fact that the female reproduc- 

 tive functions are most active when the individual is 

 actually gaining in condition. An animal that is main- 

 tained in a uniform condition of excessive fatness is not 



1 Bell, Journal of Heredity, vol. V, p. 47. 



