FERTILITY 595 



and then suddenly transferring them to an aquarium stocked 

 with growing plants and provided with running water, these 

 animals could be induced to spawn within a few days. (Cf. also 

 Annandale's observations referred to on p. 22.) Bles draws the 

 conclusion that the difficulty so often experienced in inducing 

 Amphibians to breed in a state of captivity is not due to toxic 

 influence on the gonads resulting from the confinement, but 

 must rather be ascribed to the absence of the necessary external 

 stimuli without which the generative organs of animals are 

 incapable of properly discharging their functions. Bles suggests 

 that this view may help to explain why some animals {e.g. insects) 

 make their appearance in great numbers in one year, and are 

 comparatively scarce in another. 



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

 domestication or under confinement, it is probable that nutrition 

 plays the chief part (though by no means the sole part) in re- 

 gulating the capacity to produce ofEspring. That an insufficient 

 or markedly abnormal diet must afEect this power is almost 

 self-evident, and Chalmers Watson ^ has shown that sterihty is 

 a common condition among caged rats when fed exclusively 

 upon meat. It is also certain that an excessive quantity of 

 nutriment is likewise prejudicial to the proper discharge of the 

 reproductive functions. No better example could be given of 

 the way in which overfeeding results in a condition of sterihty 

 than that of the barren Shire mares, which in recent years have 

 been a striking feature at agricultural shows in England. Some 

 foods are said to induce sterihty more easily than others. Sugar, 

 molasses, and hnseed are noted for having this effect when given 

 to cattle, but they are often used to prepare beasts for show 

 or sale, since they produce a good coat of hair and cause a 

 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, for the author has often found large quantities 

 of bright orange-coloured lipochrome in the interstitial tissue 



' Campbell and Watson, "The Minute Structure of the Uterus of the Bat,' 

 &c., Proc. Phya. Soc, Jour, of Phys., vol. xxxiv., 1906. 



