168 DISEASES OF THE HORSE’S FOOT 
repeated expansion of the wall posterior to the crack, with 
the portions anterior to it in a state of enforced quiescence, 
leads in time to the posterior edge of the crack coming to 
lie over that of the anterior. 
Complications.—The first complication likely to arise in 
a case of sand-crack is that attending simple laceration 
of the sensitive structures in a deep lesion. With the 
laceration all the phenomena of a repairing inflammation 
make their appearance. As a result, there is more or less 
heat according to the degree of inflammatory hyperemia, 
swelling according to the amount of inflammatory exudate, 
and pain according to the amount of pressure the two fore- 
going bring to bear on the nerves in the inflamed area. 
A second and more serious complication is the greater 
inflammation set up by the introduction into the crack 
of foreign substances. Small portions of gravel and flint, 
both by the irritation set up by their friction and by the 
infection they carry in with the dirt surrounding them, are 
responsible for the mischief. 
When, from direct communication with the blood-stream, 
due to extensive hemorrhage, bacteria from the outside gain 
entrance, this simple inflammation is further complicated 
by the formation of pus, or a limited gangrene of the 
keratogenous membrane. 
In cases of great severity the gangrene of the kerato- 
genous membrane spreads until the deeper structures are 
involved. We then get a necrosis (in the case of toe-crack) 
of the extensor pedis, and sometimes caries of the os pedis. 
In like manner the necrotic changes occurring under 
these circumstances may invade the deeper structures in 
the region of quarter-crack. As a result of this, we may 
have the starting-point of suppurating corn, or necrosis of 
the lateral cartilage—in other words, cartilaginous quittor. 
Commonly accompanying quarter-crack is the condition 
of contracted heels and atrophied frog. Sometimes de- 
scribed as a complication of sand-crack, it appears to us 
more rational to rather regard the sand-crack as a result 
or complication of the vice of contraction. 
