168 PRINCIPLES Otf STOCK-BREEDING. 



the action of the various modifying influences to which 

 they are subjected. In the cases of impaired fecun- 

 dity in animals that have been bred in-and-in, it will 

 be necessary to ascertain the extent to which these 

 obvious causes of a defective performance of the 

 reproductive functions are operative, before we are 

 justified in assuming the existence of some " occult " 

 or mysterious influence arising from consanguinity. 



Mr. John Wright, who is often quoted as an oppo- 

 nent of in-and-in breeding, has evidently overlooked 

 the existence of the more obvious causes of sterility 

 and barrenness, and assumed that they are produced 

 only by close breeding. 1 



He apparently concludes that, when two facts are 

 associated in a large number of cases, they must have 

 the relation of cause and effect. The most striking 

 case cited in support of his theory is as follows : 



" In pigs, the writer's experience was considerable, 

 in breeding from three or four sows at the same time, 

 all descended from the same parents, boar and sow ; 

 these were put to the same boar for seven descents or 

 generations ; the result was, that in many instances 

 they failed to J)reed^ in others they bred few that 

 lived ; many of them were idiots had not sense to 

 suck ; and, when attempting to walk, they could not 

 go straight. The last two sows of the breed were sent 

 to other boars, and produced several litters of healthy 

 pigs. In justice to the advocates of the in-and-in prin- 

 ciple, it is but right to state that the best sow during 

 the seven generations was one of the last descent. She 

 was the only*pig of that litter. She would not breed 



1 Journal of the Royal Agricultural Society, vol. vii., pp. 204, 205. 



