68 THE HORSE 



thing is "^Tong, a blister composed of biniodide of 

 mercury, one part ; lard, four parts, should be im- 

 mediately well rubbed in. The horse must have 

 absolute rest and a light diet, and should be fit 

 for work again when the effects of the blister 

 have worn off. 



Spavin 



(See Fig. 26.) This complaint must not be con- 

 fused with bog spavin, to which it is not even re- 

 motely allied. Bone spavin, as we Avill call it to 

 avoid confusion, is extremely common in some 

 districts, and is much more prevalent in some 

 breeds of horses than others. Actually it may be 

 defined as a bony enlargement found on the inside 

 and lower part of the hock, due to disease. 



To understand the exact nature of bone spavin, 

 we must return to a study of the horse's hock. 

 As already mentioned, it is usually composed of six 

 bones, sometimes of seven, according to whether 

 certain of the bones are naturally fused together, 

 or separate, or altogether absent. As evolution- 

 ists are well aware, the horse is descended from a 

 five-toed ancestor, and the two splint bones are 

 rudiments of tv\^o additional toes. As evolution- 

 ary changes are always much retarded, if not en- 



