STOCK BREEDING INDUSTRY. 21 



in the germ cells. This is the highest goal of the practical 

 breeder. But in sexually reproducing organisms like the 

 domestic animals purity of the germ cells with respect to the 

 determiners of any character is only to be obtained, in the 

 hands of a practical breeder without special scientific training, 

 by the practice of inbreeding. 



It should be clearly understood that indiscriminate inbreeding 

 without definite purpose or reason is not advised or advocated. 

 What we do mean is this : all successful breeding is the work- 

 ing out of carefully made plans looking toward the attainment 

 of a definite ideal. In those plans narrow breeding has a place. 



Introduction of new blood for purposes of rejuvenation or 

 reinvigoration is, as ordinarily done, one of the surest ways 

 to prevent any real or permanent improvement of stock by 

 breeding. The difficulty here is that when one introduces new 

 blood he runs the risk of introducing a whole set of characters 

 inferior in their degree of perfection to what he already has 

 in his own stock. As a matter of fact the average breeder is 

 usually much too ready to introduce now blood. If one is 

 breeding in certain definite blood lines and getting good results 

 he should be exceedingly conservative about introducing any 

 new blood, and should only do so when he has absolutely sure 

 evidence that it is actually necessary for one reason or another. 



There are two main reasons which induce the breeder to go 

 out after new blood. The first is a fear of the evil conse- 

 quences of inbreeding. This fear is usually, in- the particular 

 case, absolutely without foundation in fact. Yet how widely 

 prevalent is the idea among the cattle breeders of Maine that 

 at least as often as once in every three or four years one must 

 go out and buy a new bull. It passes all comprehension that any 

 intelligent person could expect to make steady progress in 

 breeding on such a system. 



Again the careful breeder sometimes finds himself in this 

 situation. He has by well planned and executed breeding 

 brought his stock up to a particular level of excellence. There 

 the improvement stops. His animals breed true to that par- 

 ticular degree of quality but cannot be made to attain a higher 

 ■degree. In other words, he has substantially purified his stock 



