596 OPERATIONS ON THE FOOT. 



and width is considerably increased. The last of these conditions 

 is a sure sign that the disease has spread under the wall of the 

 quarters and of the heels, and has produced the complete separa- 

 tion of the bars from above and below. When percussed, the 

 hoof at the heels gives a duU sound. The excessive length is only 

 an indirect consequence of the disease, and is due to the fact 

 that, so as to keep the animal at work, the walls are spared as 

 much as possible by the blacksmith, so as to avoid the contact of 

 the protruding parts with the ground. 



Physiological signs are almost entu'ely absent in canker. It 

 is a curious fact that the sensibihty which is generally highly in- 

 creased in all affections of the foot, even in chronic diseases, re- 

 mains always so obscure in canker that animals may be used for 

 a long time without lameness, though the sub-horny tissues have 

 become quite unprotected over a large surface. 



Complications. — Very frequently, canker is complicated by a 

 disease of the skin, analogous to it, known as grease ; a disease 

 which, if not entirely of the same nature, as admitted by Plasse, 

 Megnin, etc., is closely related to it. It is often through this 

 that canker begins, and very often the two diseases exist together 

 in the same animal, one sometimes following the other, just as 

 canker of one foot follows that of another. 



Among the complications of canker, as generally admitted, are 

 some injui'ies of the plantar cushion : inflammation and necrosis 

 of cartileges, ligaments or tendons, and even caries of the os pedis 

 and anchylosis, which are sometimes observed ; however, a close 

 examination of the facts allows us to say that these accidents do 

 not arise under the simple influence of the disease alone, but that 

 they are due to the improper use of sharp instruments, of the 

 actual cautery, and especially of potential caustics. As La Gueri- 

 niere said, the deep lesions of tendons and of the os pedis, which 

 are observed in severe cankers, have no other cause than the 

 action of too powerful dessicatives. 



Duration, march, termination. — Canker is an essentially chronic 

 disease, and may be of long continuance, even lasting for years. 

 Still, under this heading there are many variations, whose cause 

 it is difficult to find. There are horses whose disorganization of 

 the hoof is complete after two or three months. There are others 

 where the disease remains stationary for more than a year. We 

 have seen it remaining limited to one lacuna for months, and all 



