INFLAMMATORY AFFECTIONS 311 
keratogenous membrane, leading to abnormal secretion, 
and, in place of the horny cells it should normally secrete, 
is thrown out an abundance of a serous fluid. 
This upraised and softened horn once thrown off is not 
again renewed, and the whole of the sensitive frog and 
perhaps a portion of the sensitive sole is left uncovered. 
In place of the normal horn, however, is often found a 
hypertrophy of the elements of the keratogenous membrane 
leading to huge fungoid-looking growths with a papillo- 
matous aspect, damp in appearance and offensive in smell, 
and readily bleeding when injured (see Fig. 184). 
The horn immediately surrounding the lesion is loose 
and non-adherent to the sensitive structures. This in- 
dicates, of course, that the disease has spread further 
beneath the horny covering than is at first sight apparent. 
Portions of this loose horn removed reveal beneath it a 
caseous fcetid matter, easily removed by scraping (the per- 
verted secretion of the keratogenous membrane). When 
this is carefully scraped away, the sensitive structures 
appear to be covered with a thin, smooth membrane, gray 
in colour and almost transparent, while beneath it may be 
seen the red appearance of normal sensitive structures. 
If the horn surrounding the lesion is not touched with 
the knife, but little is seen of the extent of the disease, for 
that removed by natural means is often very small in 
quantity. To all intents and purposes the disease appears 
to be confined to the frog. This appearance is misleading, 
especially if the disease has been in existence for some time, 
for it may have easily spread to the whole of the sole, and 
even to the greater portions of the lamine secreting the wall. 
Tt is, in fact, not until the pressure exerted by the 
normal horn is removed by its breaking away that the 
vascular structures of the keratogenous membrane begin 
to swell, and the perverted secretions to enlarge in size. 
Once the pressure is removed, however, this quickly comes 
about, and the characteristic fungoid growths rapidly make 
their appearance. 
This tendency to spread is highly indicative of canker. 
