. La biologie et la vie humaine. La biologie. La sélection des animaux 525 Mort de vaste. Bovins le brahmane de l'Inde, cependant, sont à l'abri de la fièvre du Texas. Lorsque ces ani- immunitaire mals sont accouplés à la va- rieties sensibles, l'hybrides sont tous les im- mune ; c'est l'immunité, dans ce cas est dominante. Brahmin bovins ont été importés en consé- quence de croisement avec notre na- tion bovins, afin d'établir une variété ayant la qual- ités de boeuf de variétés américaines avec l'immunité à la fièvre du Texas 150 ^entre-temps, il a été constaté que la fièvre du Texas est transmises par un petit animal

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. Biology and human life. Biology. 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.. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and

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