632 THE PHYSIOLOGY OF REPRODUCTION 



deposit of fat. Very fat animals do not come in season so often, 

 and consequently cattle " settle better and feed faster as they become 

 what the butchers designate ' fat ripe.' " In such animals there 

 can be no doubt that the ovarian metabolism is abnormal, and the 

 author has often found large quantities of bright orange-coloured 

 lipochrome in the interstitial tissue of the ovaries of fat cows and 

 heifers. 1 Kirkham z records sterility in white and yellow mice which 

 after four to six litters lay down extensive quantities of fat and 

 thenceforward fail to breed. In man also obesity is known to be a 

 cause of sterility, in the male spermatogenesis being partly inhibited. 3 



A low condition, especially if associated with' exposure to wet and 

 cold, as in the case of cattle wintered in the open air, or of cows 

 which have suckled a large calf or more than one calf, is also a 

 common cause of temporary barrenness. 4 Certain other more special 

 causes of sterility are referred to briefly below (p. 644). 



A few years ago the Royal Agricultural Society of England 

 instituted an inquiry into the subject of fertility in sheep. The 

 investigation was conducted by Heape, at whose instigation it was 

 carried out. In the report/ which was subsequently published a 

 comparative account is given of the fertility of various breeds of 

 sheep chiefly in the South of England in the season 1899. The most 

 fertile breed was the Wensleydale, in which six flocks, consisting of 

 a total of 319 ewes, produced a percentage of 177'43 lambs. The 

 effects of locality are disciissed, and there is an accumulation of 

 evidence indicating that the character of the district is not without 

 influence on the fertility of the breed. Thus, Lincoln sheep run on 

 the wolds, Shropshire sheep on a subsoil of New Red Sandstone, and 

 Hampshire sheep, which are not run upon chalk downs, are shown 

 to be associated statistically with a relatively high percentage of 

 infertility. The report shows further that the fertility of a flock 

 depends greatly upon its management, that the quality and quantity 

 of the food supplied affect the condition of the sheep, and so influence 

 their power to breed, that some seasons are more favourable to 

 fertility than others, and that sheep-stained pasture (or pasture 

 on which sheep have run for some considerable time previously) 

 is detrimental to breeding stock. 



1 Marshall and Peel, "Fatness as a Cause of Sterility," Jour. <>/' A >jn'<: Seiettee, 

 vol. iii., 1910. The lipochrome may have belonged to persistent corpora lutea. 



2 Kirkham, "The Life of the White Mouse," J'ro,: iSbft K.<- r . />'/./. and Med., 

 vol. xvii., 1920. 



3 Cooper, The Sexual Disalrilitirs of Man, London, 1018. 



4 Wallace (R), Farm Lire Xtnck ,,f (1,-,-at Britain, 4th Edition, Edinburgh, 

 1907. 



Heape, "Abortion, Barrenness, and Fertility in Sheep," Jov/: Il<>,/. A <>//>: 

 A.V*-., vol. x., 1899. See also Heape, " Note on the Fertility of Different Breeds 

 of Sheep, etc., r r ,-<. //_,/. >'<-., vol. Ixiv., 1899. 



