VENTILATION OF STABLES. 51 



of e^ery existing species, it has been ordained, that, when 

 placed under certain conditions, some shall die that others 

 may live. When a class of animals' become so excessively 

 numerous that something essential to its existence, such as 

 air, food, or water, is in danger of being exhausted, a disease 

 quickly arises, which carries off a certain number, perhaps a 

 majority of the claimants. Those which survive have suf- 

 ficient, though it may be a scanty subsistence ; while, had 

 all lingered on, all must have perished, and the race would 

 be extinguished. In relation, however, to animals which are 

 spread over the earth so extensively as the horse, this law 

 is probably intended to prevent excessive multiplication, 

 rather than to preserve the species, which could hardly be 

 all endangered in so many different places at the same time. 

 As yet, the existence of such a law has been little observed, 

 and numerous examples of its operation can not be cited. 

 " On some of the dry and sultry plains of South America," 

 says an excellent writer, " the supply of water is often scanty, 

 and then a species of madness seizes the horses, and their 

 generous and docile qualities are no longer recognised. They 

 rush violently into every pond and lake, savagely mangling 

 and trampling upon one another, and the carcasses of many 

 thousands of them destroyed by their fellows [and by the 

 disease ?] have occasionally been seen in and around a con- 

 siderable pool. This is one of the means by which the too 

 rapid increase of this quadruped is, by the ordinance of na- 

 ture, here prevented."* When a scarcity of food prevails 

 among wild animals, it is very likely that some cause arises 

 to diminish the demand. Among domestic animals, frequent 

 abortions and barrenness may in many instances be traced to 

 the famine of a severe winter. It is difficult to conceive how 

 any deficiency of air can occur to the free dwellers of the 

 forest and the desert. Yet such an event is possible ; I see 

 no absurdity in supposing that animals might congregate in 

 such extraordinary multitudes, that the air would be con- 

 taminated and become destructive of those by whom it is 

 breathed. It is said that horses have been seen in droves of ten 

 thousand. Were several of these herds by any chance thrown 

 into one, no place could afford sufficient nutriment to maintain 

 them ; and it is probable that the air would then receive 

 po\\er to destroy a few, lest famine should destroy all. It 

 may be true that nothing of this kind has ever been observed 

 to take place among any mass of untamed animals. There 

 * Mr, YouattThe Horse. Lib. Use. Knowledge, p. 8. 



