CAUSES OF CANKER. 1091 



generally overlooked. As a rule, a small raised patch first forms 

 on the frog and produces a grey, greasy, offensive material. On 

 removing the loose horn, the enlarged villi of the frog, which cause 

 the breach, can be detected with the naked eye. Lameness is rare 

 at first, a symptom of considerable diagnostic importance, for in acute 

 inflammatory diseases, great pain and lameness are always present. 

 Gradually, sometimes almost imperceptibly, the disease extends, 

 attacking first the frog, then the sole and bars, passing from these 

 to the wall, and sometimes reaching as high as the coronet ; always 

 making its way between the sensitive and horny structures, which 

 it finally separates. The sensitive laminae become enlarged and 

 converted into brush-like structures, which produce exuberant 

 vegetations immediately the wall covering them is removed. 



With the extension of the process to the bars and sole the hoof 

 expands at the quarters, whilst the frog considerably enlarges. At this 

 stage lameness is sometimes seen during movement, but this is probably 

 due to loss of the horny covering and accidental injury, not to the 

 diseased process. When the condition is neglected it continuously 

 advances, until finally it affects the entire matrix, causing great 

 deformity of the hoof. 



Causes. The causes of canker are at present little understood, 

 and opinions as to the nature of the disease vary greatly. The name 

 is a very old one, and originated at a time when it was customary 

 to describe many different disease processes, distinguished by their 

 malignant character, by the same term. It has long been recognised 

 that canker has no real relationship with carcinoma, and therefore, 

 strictly speaking, the name is unjustifiable. The disease is commonest 

 in animals of a lymphatic temperament, and is favoured by dirty, 

 ill-drained stables, where animals stand continually on litter soiled 

 with manure, and saturated with decomposing, ammoniacal urine. 

 Canker is probably due to specific infection, as seems indicated 

 both by its course and the manner in which it reacts to treatment, 

 but the infection does not appear to be due to a single organism, 

 but to several, which do not always agree in their method of action. 

 Megnin has described one which he terms Keraphyton. (The subject 

 receives further attention in Dollar and Wheatley's book on " Horse- 

 shoeing and the Horse's Foot.") 



Prognosis. Although canker always takes a chronic course, yet it 

 shows many variations which are of real importance in forming a 

 prognosis. Under any circumstances the practitioner should be 

 cautious in giving an opinion, though the greater number of cases 

 recover. The more active the process in the rete tissue and papillae, 



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