IMMUNITY TO DISEASE 



345 



of wheat was between 10 and 15 bushels per acre. By selection and 

 cultivation, the yield per acre has been increased to over 40 

 bushels. Wheat has been bred so that several species now combine 

 the desirable qualities of large yield per acre, good quality for 

 bread making, hardiness, resistance to rust, and resistance to 

 drought. The ordinary corn stalk usually produces but two or 

 three ears. But through experimentation, corn has been produced 

 with stalks 16 feet high and which bears 32 ears to the stalk. 



The particular aims of plant and animal breeding are to 

 establish varieties immune to disease, to produce new species, to 

 breed for desirable characters, to improve quality by proper selec- 

 tion and to make both old and new forms more productive. 



Immunity to disease. In some of the Southern States, the 

 cattle had long been subject to Texas fever which was easily 

 spread and caused the loss of 

 many cattle. It was learned 

 that the wild Brahmin cattle of 

 India were immune to the dis- 

 ease. Their jlesh, however, 

 was not valuable as beef. Two 

 strains, our southern cattle 

 and the wild Brahmin, were 

 crossed. Immunity to Texas 

 fever was found to be domi- 

 nant in the FI generation. 

 These hybrids were mated 

 again and from the F2 genera- 

 tion only the immune animals 

 that seemed to show the best 

 beef tendencies were selected 

 and bred. By careful selection 

 a species of cattle combining both immunity and good beef 

 qualities was thus obtained. 



WH. FITZ. AD. BIO. 23 



U. S. Dept. of Agric. 



Animal breeders have produced from the orig- 

 inal wild strain of pig shown above the fine 

 specimen shown below. Compare the food value 

 of the two specimens. 



