Predisposing Causes of Roarivg. 45 



her dam, who were both Roarers ; the first had a filly by 

 Sorcerer, which in time exhibited the same defect, and 

 transmitted it to her son, Black Jack. Marry produced 

 three Roarers by three different horses. Markhami gives 

 an instance in which, of eight descendants from a Roarer, 

 six became affected. 



Pedigree horses of the heavier breeds, such as shire and 

 Clydesdale cart-horses, have sometimes this hereditary 

 weakness. 



The transmission of predisposition is, of course, more cer- 

 tain when both parents are affected than when only one is 

 a Roarer ; in the latter case the chances are more in favour 

 of the progeny escaping, especially if circumstances are 

 otherwise propitious. Besides, the hereditary influence is 

 not equally manifested in all the produce from the same 

 stock, as there are often many exemptions, only one-half 

 or one-third becoming affected when exposed to exciting 

 causes. 



It has also been remarked that age appears to influence 

 the potency of hereditary predisposition in such a manner, 

 that a stallion affected with Roaring will beget fewer foals 

 with the tendency to that weakness when young than when 

 old. A remarkable example is given by Charon, of the 

 Haras stallion, Pater, which was a Roarer. Very few of the 

 produce of his earlier years became affected, but nearly all 

 those he begot in his old age were Roarers when young. 



But in considering this question of heredity, it must be 

 confessed that a satisfactory conclusion cannot always or 

 easily be arrived at. The predisposition may exist, but the 

 immediate exciting cause may never arise ; while certain 

 diseases occurring in horses which may not have the pre- 

 disposition are often followed by Roaring. When the 

 defect appears at a very early age, and without any marked 

 €xciting cause, then predisposition may be suspected. 



Goodwin, quoted by Percivall, gives the case of the cele- 

 1 " The Veterinarian," 1839. 



