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 lacera- 

 tion 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, swell- 

 ing 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 haemorrhage, 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 spreds 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. 



