164 DISEASES OF THE HORSE'S FOOT 



animal at fast work over -reaches. The secretion of horn at 

 the injured coronet is interfered with, a diminished supply 

 at an isolated spot being the result. From this point 

 grows down a fissure in the wall. 



An injury of the same character may also be sustained 

 in various other ways — treads from other animals when 

 working in pairs, accidental wounding with the stable-fork, 

 blows of any kind, or a self-inliicted tread with the calkin 

 of an opposite foot — each with the same result. 



So far as causation is concerned, toe-crack stands in a 

 class almost by itself. It is met with nearly always in a 

 heavy animal in the hind-foot, and is directly attributable 

 to the force exerted in starting a heavy load. 



Unskilful shoeing also plays a part in the causation of 

 sand-crack. Removal of the periople by excessive rasping 

 of the wall is most certainly a predisposing cause. Cracks, 

 or their starting-points, may also be caused by using too 

 wide a shoe, or by the use of nails too large in the shank. 

 Also, they may arise from unskilful fitting of the toe-clip, 

 especially in the hind-foot of a heavy animal. It must be 

 admitted, however, that the part shoeing plays in the 

 causation of sand-crack is not a large one ; far more 

 depends upon the state of the horn and the animal's con- 

 formation than upon the exciting cause. 



So far, our observations on the causes of sand-crack have 

 referred to that form occurring in the wall. Sand-crack of 

 the sole or frog we have already said is but seldom met 

 with, and then it is always in connection with some ex- 

 ceptionally deteriorated quality of the horn, as in the case 

 of badly pumiced feet, or occurs as a result of direct injury. 

 Extensive slit-like cuts in this region, when deep enough 

 to lacerate the keratogenous membrane, are sometimes 

 followed by the growth of a fissure in the horn, and what 

 might almost be termed a permanent sand-crack results. 

 Such cuts may be occasioned by sharp flints, broken glass, 

 or other sharp objects picked up on the road, or may result 

 from the animal treading on the toe-clip of a partially cast 

 shoe. 



