ANIMAL BREEDING 



525 



death of vast num- 

 bers. The Brahmin 

 cattle of India, how- 

 ever, are immune to 

 Texas fever. When 

 these immune ani- 

 mals are mated with 

 the susceptible va- 

 rieties, the hybrid 

 offspring are all im- 

 mune; that is, im- 

 munity in this case is 

 dominant. Brahmin 

 cattle were accord- 

 ingly imported for 

 crossing with our na- 

 tive cattle, in order 

 to establish a variety 

 having the beef qual- 

 ities of American 

 varieties with the 

 immunity to Texas 

 fever .1 



^In the meantime it 

 has been found out that 

 the Texas fever is trans- 

 mitted by a little animal 

 known as the tick, which 

 sucks the blood from the 

 diseased cattle. By suit- 

 able quarantine it has 

 been possible to restrict 

 the Texas fever; and by 

 applying to the bodies of 

 the cattle something that 



Fig. 219. The law of unit characters 

 illustrated by guinea pigs 



Pigmentation in these animals is dominant over albi- 

 nism. Short hair is dominant over long hair. Rough 

 coat is dominant over smooth coat. When two pure 

 individuals like those shown are mated, the offspring 

 will be short-haired, dark, and rough-coated. On mating 

 the hybrids together in sufficient numbers the segrega- 

 tion will result in producing every combination of 

 these three sets of characters: dark-short-rough; dark- 

 short-smooth; dark-long-rough; dark-long-smooth; 

 white-short-rough; white-short-smooth; white-long- 

 rough; white-long-smooth. The proportions will be 

 such that for each pair of contrasted characters there 

 will be one recessive to every three dominants. (From 

 photographs lent by Professor W. E. Castle) 



will either kill the ticks 



or prevent their biting the cattle, it may be possible to eradicate this costly 

 disease. But if we could replace our present herds of cattle with a type that is 

 quite immune, the added cost would no doubt be made up in a very short time. 



