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Hereditary Diseases of Horses. 



which gives a mechanical advantage to the tendons passing over 

 it. With the aid of this lever the tendons perform the work 

 required of them with ease and safety : without it, they are apt 

 to suffer from the sudden and violent shocks to which they are 

 subjected, especially when the horse is put to fast work. 



Navicular Disease depends upon strain or laceration of the 

 tendo perforans just where it passes over the navicular bone. It 

 causes pain and tenderness of the parts affected, a short, tripping, 

 but cautious gait, a wiring in of the heels, and a wasting of the 

 muscles of the shoulder, with all the other well-known symp- 

 toms of grogginess. The predisposition to this disease is espe- 

 cially great in horses with narrow chests, upright pasterns, and 

 out-turned toes. Even with average work, horses in which this 

 conformation is decided can scarcely fail to become groggy, for 

 the distance between the point at which the tendo perforans is 

 inserted into the os pedis and that at which it passes over the 

 navicular bone is so short, and the angle it makes so acute, that 

 the tendon acts at a mechanical disadvantage, and is constantly 

 liable to strain. But defects like these rarely occur singly, there 

 usually existing in addition a want of mutual adjustment between 

 other parts of the limb. Navicular disease is, therefore, to a 

 certain extent hereditary, in so far as there are certain forms of 

 limb especially subject to it. A tendency to it exists in several 

 stocks that have come under my own observation ; and I am in- 

 formed by a veterinary friend, Mr. Tuthill, long resident in Ire- 

 land, that he knows of the progeny of several Irish horses, in 

 which navicular disease is so common, that they are always looked 

 upon with suspicion, and bring in consequence lower prices than 

 their general appearance would otherwise warrant. The progeny 

 of "Young Musician," for example, a thorough-bred horse, well 

 known in Ireland, and especially in the western counties, all 

 show a great tendency to this disease. 



Acute diseases are usually referable to some cause or causes 

 which are often violent in their nature, but operate for a com- 

 paratively short time ; their special locality may be determined, 

 or their type or intensity modified, by the particular constitution 

 of different animals ; they seldom, however, owe their existence 

 to inherent hereditary causes. Chronic diseases, on the other 

 hand, usually result from the continued operation of causes 

 inadequate to induce acute maladies ; they often occur as conse- 

 quences of badly-treated or acute attacks, their development is 

 greatly dependent upon the special constitution of the indi- 

 vidual, and many of them are more or less hereditary. No dis- 

 eases better illustrate this than those affecting the respiratory 

 organs, such as chronic cough, thick -wind, and roaring, all of 

 which are usually hereditary. 



