368 THE t^AkM DOCTOR. 



mass of soft, spongy, yielding horn between the horny laminfe 

 and the hoof-wall, causing a falling in of the wall anteriorly, 

 and a descent of the margin of the coffin-bone so that it will 

 press upon and even perforate the sole {pumice foot). In other 

 cases there is merely a circumscribed horny growth, pressing 

 inward on the quick at a particular point {keraphyllocele). It 

 :he secreting surface ot the sole is involved similar horny 

 tumours may be formed, as in corns. Disease of the secreting 

 membrane of the frog may determine an unhealthy secretion 

 from the cleft {thrush), or an excessive growth and loss of 

 cohesion of the horny fibres {canker). 



In addition to these disorders originating in the deeper 

 structures we have a further list that take their origin in un- 

 natural states of the horn. And for these the current modes 

 of shoeing are mainly chargeable. 



At all points the hoof undergoes a steady condensation from 

 its inner to its outer layers. In a transverse section of the 

 hoof-wall the deeper tubes are open, spacious, and surrounded 

 by soft, yielding, elastic horn, while those near the surface are 

 exceedingly minute, and surrounded by a far greater amount of 

 dense, hard, and exceedingly resistant horny matter. The 

 outer surface is especially close in its texture, and as the tubes 

 run through the whole length of the wall to its IoW(3r or wearing 

 buriace, where they are closed by attrition, comparatively little 

 exhalation of moisture can take place from this part of the horn 

 in its healthy state. But it is far different when the dense 

 surface layer has been removed by the rasp, and the open ends 

 of the tubes exposed all over the surface of the wall. Then 

 evaporation and drying go on rapidly, the hoof becomes hard 

 and brittle and follows its constant tendency, whin dry, to turn 

 in at the heels and coronet, causing absorption of the parts 

 beneath and laying the foundation of disease. 



The sole and frog naturally increase in density from the quick 

 outward but the h -irn breaks up into pbtcs before becoming 



