CANKER OF THE SOLE AND FROG. 
S15 
bandage. If proliferation from the surface of the sensitive structures 
proves troublesome nitrate of lead may be employed; Schleg used the 
actual cautery. The above-described dressing should then be applied 
and left in position for some days. When changing it, the parts are 
carefully examined, and if the wall has become further undermined 
the affected horn should at once be removed, but as a rule there is 
no marked tendency to extension, a feature which further distinguishes it 
from canker. 
III.—CANKER OF THE SOLE AND FROG (PODODER- 
MATITIS CHRONICA VERRUCOSA YEL MIGRANS). 
Since olden times a chronic inflammatory disease of the horn-secreting 
structures of the foot, which shows a strong tendency to extend and seize 
on fresh areas, has been recognised and generally described as canker. 
The disease consists essentially in chronic proliferation in the papillae 
and tissue of the rete, the papillae becoming enlarged and the cellular 
elements of the rete undergoing active increase. True horn production 
is thus checked, the epithelium produced not forming horn, but breaking- 
down and producing a greasy, stinking grey fluid. As pointed out in 
speaking of “ grease,” the disease is identical in character with so-called 
grease, i.e., it consists in a dermatitis verrucosa : it has also been stated 
that either condition may produce the other, i.e, that grease may cause 
canker, and canker grease. Both conditions are very obstinate. 
Symptoms and course. The commencement of the attack is generally 
overlooked. As a rule, a small prominence first forms on the frog and 
produces a grey, greasy, offensive material. On more careful examina¬ 
tion the enlarged papillae of the frog, which cause the swelling, 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. In the sensitive laminae 
the process produces similar changes to the inflammation described in 
last chapter. 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 over rough or even 
over soft ground, but this is probably due to loss of the horny covering 
