Cxiv INTRODUCTION. 



pairment of the constitution of the animals, and at length 

 in unfitting them for reproducing their own kind. In the 

 practice which has existed in England of forming artificial 

 breeds of sheep and cattle, this class of experiments has 

 been made to the degree of shewing the limits to which 

 it can be carried, under a regard to the safety, and even 

 existence, of the animals. In the original formation of some 

 of the finer artificial breeds of this country, animals were 

 sought for having the characters which it was designed to 

 cultivate. But the breeders, unwilling to mix the blood of 

 inferior races with that of their own improved stocks, con- 

 tinued to breed from them alone, and found, by experience, 

 that the nearer in affinities of blood, and consequently of 

 characters, the parents were, the more their progeny re- 

 sembled them. Hence the extensive system of breeding 

 " in-and-in," as it was called, pursued by the earlier breed- 

 ers, as Bakewell, Colling, and others. The effect was very 

 quickly to produce a distinct family, distinguished by the 

 characters communicated to it. But this effect was followed 

 by another which was not contemplated, and could scarcely 

 have been inferred independently of experience. The ani- 

 mals arrived sooner at maturity, and thus became more 

 quickly adapted to the uses for which they were intended, 

 the supply of human food : so that one of the most import- 

 ant ends of the breeder was attained, the procuring of ani- 

 mals fitted to arrive at early maturity of muscle and fatness, 

 in which respects some of the artificial breeds of England 

 became the finest in the world, and still surpass those of any 

 other country. But the practice was soon discovered to have 

 its limits, and, when carried too far, to produce all the effects 

 on the system which have been referred to. The animals, 

 with their earlier maturity, and increased tendency to obe- 

 sity, became less hardy ; their skins became thinner, and 

 the hairy or woolly covering more scanty ; their limbs be- 

 came more slender ; the males lost so much of the masculine 

 characters as often to be incapable of propagating their race, 



