464 CSAPTEE 61 



horn fibres having been destroyed, the nails have a less firm hold and 

 consequently the shoe is more easily pulled off, and probably a consider- 

 able portion of the weakened crust will come away with it. 



945. Why then do farriers rasp the Crust ? 



First, because an apparently good fit of the shoe to the foot is essen- 

 tial. Secondly, because it is easier to produce to the eye of an inexperi- 

 enced person the appearance of a good fit by rasping down the foot to a 

 shoe rather too small for it than to fit the iron to the real size and shape 

 of the foot. 



The primary essential of all good shoeing is that the outside of the 

 crust be not rasped. 



946. Of lowering the crust versus rasping its exterior surface. 



The crust or wall having been protected by the shoe from that natural 

 friction and wear against the ground to which it would have been sub- 

 jected if it had not been so protected, it is necessary each month to lower 

 the crust as much as will represent what would have been the natural 

 detrition by wear. 



How much this will be must vary in different horses. In some feet 

 the growth is much more rapid than in others. In some hoofs of soft 

 material the crust wears away considerably, even though protected by a 

 shoe. This question must be left to the practical and practised eye of 

 the farrier. 



But it will be asked, How is the crust to be lowered without causing 

 the injuries described above to its structure? 



Simply by removing all that requires to be removed from the inferior 

 or ground surface of the crust, without touching the superior part. This 

 will be best done by the rasp from underneath, though, if the crust be 

 very long, the knife may be used (A, fig. 4). 



After a sufficient quantity has been removed, the inferior or ground 

 surface must be made perfectly level, for the reception of the shoe, by 

 tne use of the rasp. 



The strength of the fibres of the crust will not be in any degree less- 

 ened by shortening them. On the contrary, it will be rather increased. 

 Let me illustrate what I mean by an ordinary quill or pencil. If I shave 

 it longitudinally it will be weakened as regards its power of sustaining 

 weight on its top ; but if I cut half an inch or an inch off its lower end 

 it will practically be strengthened. For illustration see A, figs. 2 and 3, 

 as compared with A, fig. 4." 



947. Prevention of splitting of the Crust after leing lowered. Feather 



edge. 



When the crust has been sufficiently lowered and made level by the 

 rasp, as above described, it will be sharp all round its exterior circle. 

 This sharp or feather edge must be removed by the rasp before the shoe 



