138 INTRODUCTION TO SEXUAL PHYSIOLOGY 



litters than wild animals belonging to the same species. On the 

 other hand, certain wild animals, when removed from their 

 natural conditions and brought into captivity, become partially 

 or com2:>letely sterile ; the Indian elephant, for example, seldom 

 breeds under domestication, although kept in a perfectly healthy 

 condition and in its native country. It would seem that in the 

 absence of the normal stimuli the generative system somehow 

 fails to discharge its functions, and this failure ma}^ take the 

 form either of absence of sexual desire (impotence) or of incapacity 

 to produce active spermatozoa or ripe ova. 



In animals which, as a general rule, breed freely in a state 

 of confinement or domestication, there is no doubt that nutrition 

 plays a very leading part in regulating the capacity to produce 

 offspring. Very fat animals not only have fewer young, but come 

 on heat less frequently. In the male spermatogenesis is partially 

 inhibited. In the female there is a greater amount of follicular 

 atrophy, the ovarian metabolism being disturbed by the deposi- 

 tion of fat. Follicular atrophy is likewise common in under-fed 

 animals, and may take place as a result of suckling. It is known 

 also that menstruation in women, as well as the capacity to pro- 

 duce ripe ova, are liable to be inhibited by lactation, but this 

 is by no means invariable. 



The practice of " flushing " sheep, that is, supplying them with 

 cake or corn or turnips, or putting them on superior pasture, for 

 a few weeks before and during the sexual season, is well known 

 to result in a larger crop of offspring at lambing time. This is 

 because it induces a larger number of follicles to ripen and of 

 ova to be discharged at the a^strous periods. Once the ewes 

 have become pregnant, the/' flushing " may be discontinued, since 

 the number of embryos has been already determined at ovulation. 

 It is recognised also that a good thriving or improving condition 

 at the sexual season in any farm animal is the one most satis- 

 factory for getting the maximal number of young. 



FcETAL Atrophy 



In some domestic animals, however, and more particularly 

 in the sow and tame rabbit, which produce large litters and not 

 one or two (or less commonly three), as in the sheep, fecundity 

 may be conditioned rather by the factors controlling development 



