306 DISEASES OF THE HORSE'S FOOT 



With restoration, so far as is possible, of the frog functions, 

 and with careful dressing, a cure is nearly always obtained. 



6. Canker. 



Definition. — Under this unscientific, yet expressive term, 

 is indicated a chronic diseased condition of the keratogen- 

 ous membrane, commencing always at the frog, and slowly 

 extending to the sole and wall, characterized by a loss of 

 normal function of the horn secreting cells, and the dis- 

 charge of a serous exudate in the place of normal horn. 



Causes. — The exact cause of canker has still to be dis- 

 covered. Therefore, before expressing an opinion as to 

 what the probable cause may be, we may dState here that 

 such opinion can only be based upon clinical observation. 

 Such being the case, we are almost duty bound to give the 

 views of older authors before those of more modern writers. 



From the mass of material ready to hand we may select 

 the following as serving our purpose. 



The earliest opinion appears to have been that canker, as 

 the name indicates, was of a cancerous or cancroid nature. 

 This was also believed by Hurtrel D'Arboval, who looked 

 upon canker as carcinoma of the recticular structure of the 

 foot. The same theory we find enunciated in the Veterinary 

 Journal so late as 1890. Although the word ' cancer ' or 

 ' carcinoma ' is not there used, the author employs the 

 terms ' Papilloma ' and ' Epithelioma ' with the evident 

 intention of expressing his belief in the malignant nature of 

 the disease. 



Another early opinion was that the disease was a spread- 

 ing ulcer, gradually extending and changing the tissues 

 which it invaded. 



A further early theory, and one which if not still believed 

 in, has died a hard death, is the constitutional theory. This 

 was believed in by nearly all the older writers, and is 

 mentioned so late as 1872 by the late Professor Williams. 

 In his ' Principles and Practice of Veterinary Surgery/ he 

 says : "Canker is a constitutional disease due to a cachexia 

 or habit of body, grossness of constitution, and lymphatic 



