PLANT AND ANIMAL IMPROVEMENT 213 



which have shown so much speed; for the Shorthorn and 

 Hereford, the most famous English breeds of beef cattle ; 

 for the Southdown and the other famous sheep breeds, the 

 Shropshire, the Oxford and the Hampshire, to which it 

 has given rise; and for almost all of the more famous 

 breeds of dogs, not even excepting the large types, the 

 mastiff, the St. Bernard, and the Newfoundland, which 

 are derived from the Tibetan dog, Canis niger, as a foun- 

 dation stock. 



Perhaps the most notable examples of conscious use 

 of intense inbreeding in developing breeds of marked ex- 

 cellence are the dairy cattle of the channel islands, the 

 Jersey and the Guernsey. One does not need to describe 

 or to eulogize these strains. What they are and what they 

 have accomplished in producing milk and butter fat are 

 known throughout the world. Starting with the cattle of 

 Normandy and Brittany as foundation stock, these two 

 breeds have been built up by persistent use of a more 

 intense system of inbreeding than is recorded in the his- 

 tory of any other strain of livestock. In fact, since 1763 

 rigidly enforced laws have prevented landing any live 

 cattle whatsoever on either island except for slaughter. 

 When one realizes that the larger of these two islands, 

 that of Jersey, is but eleven miles long by six miles wide, 

 he can appreciate the amount of inbreeding these laws 

 have promoted. 



With swine, one gathers that injurious results from 

 close mating may be somewhat more pronounced than 

 with some other animals ; in other words, that swine carry 

 a large number of deleterious recessive characters. But 

 many of the famous breeds of swine have been rather 

 closely inbred. Mr. N. H. Gentry of Sedalia, Missouri, 



