110 



Hereditary Diseases of Horses. 



haps, to the unrestrained liberty to which the race may have been 

 accustomed in Norway." * 



Much of what has been already stated concerning the heredit- 

 ary nature of the external conformation and other qualities of the 

 horse is also applicable to cattle. The progeny of a common 

 stock bear a close resemblance to their parents and to each other 

 in general appearance, length of limb, development of chest, 

 shape of carcase, position and size of the udder, adaptation for 

 the dairy, thickness of skin, and length and texture of the hair. 

 In some of the hot provinces of South America there are cattle 

 " noted for an extremely rare and fine fur. . . . The variety is 

 reproduced or descends in the stock." f In the same localities is 

 also found another race with an entirely naked skin, which pecu- 

 liarity is also hereditary. In our own country, too, there are great 

 differences in the length and texture of the hair of various sorts 

 of cattle — differences which, as in the South American animals, 

 are transmitted to the progeny. The existence or non-existence 

 of horns, their size, shape, and curvatures, are characters the 

 hereditary nature of which is generally admitted. But defects 

 and deformities may also become permanent in a stock. We 

 are informed by a friend that he has seen several cattle with a 

 small portion of skin covered with short hair situated on the eye, 

 just within its outer canthus ; and that this peculiarity had been 

 traced back for five or six generations, and had occurred in every 

 case in exactly the same spot of the right eye. 



We have deemed it advisable thus far to consider the here- 

 ditary tendencies of external form, of habit, and of constitution, 

 in order to illustrate more fully and satisfactorily the hereditary 

 tendencies of disease, which we shall now proceed to discuss. 



Hereditary diseases exhibit certain eminently characteristic 

 phenomena, some of which we shall here enumerate : — 



1. They are transmitted by the male as well as by the female 

 parent, and are doubly severe in the offspring of parents both of 

 which have been affected by them. 



2. They develop themselves, not only in the immediate pro- 

 geny of animals affected by them, but also in many subsequent 

 generations. 



3. They do not, however, always appear in each generation 

 exactly in the same form. One disease is sometimes substi- 

 tuted for another analogous to it, and this, after some genera- 

 tions, becomes again changed into that to which the breed was 

 originally liable. Thus, stocks of cattle previously subject to 

 phthisis often become affected for several generations with 



See Prichard's ' Natural History of Man,' 2nd edition, p. 72. 

 t Prichard's * Natural History of Man,' 2nd edition, p. 33. 



