PRINCIPLES OF SHOEING. 467 



be liable to cause injury to the sensitive sole. Therefore the farrier cuts 

 it away. In fact, the direction usually given is to pare out the sole at 

 each shoeing, until it will yield to the strong pressure of the thumb, 

 with a view of giving relief to the sensitive sole from undue pressure. 



In truth, however, the sole will never become unduly hard unless it be 

 pared out. Its hardness or its softness is mainly dependent on its thin- 

 ness or its thickness, except in certain diseases. 



If left in a state of nature, the thickness of the healthy sole is sufficient 

 to preserve its own inherent moisture ; but if it be made artificially thin 

 by paring the whole remaining substance will dry up and become hard. 

 On the other hand, the outer flakes, if allowed to remain, though they 

 may be apparently hard, will preserve the moisture of the inner flakes. 

 If, however, the outer flake be removed, the next flake becomes hard, and 

 60 on ; and if by constant and prcujuture removal c>f successive outer 

 flakes by the knife, the insensitive sole is made very thin, the whole 

 remaining substance will become very hard. Let me take an illustration. 

 If I take a quire of paper and soak it in water, the underneath sheets will 

 remain soft for a long time ; but if I take off each upper sheet as it 

 becomes dry and hard, the next sheet will soon become dry and hard ; 

 and if I continue the process of removal as each sheet becomes dry, the 

 lowest sheet of all will become drv and hard. 



951. Of unihie pressure on the Sensitive Sole from mutilation of the Crust 



and Frog. 



The effect of rasping the crust was pretty fully described in the early 

 part of this Chapter. The crust or wall of the foot, with the aid of the 

 frx)g, is intended by nature to sustain the greater part of the whole weight 

 of the frame. If the crust be weakened by rasping and thereby rendered 

 insufficient to sustain the weight, a portion of the weight will come on 

 the sole at the part not intended by nature to bear weight or pressure 

 (b, fig. 2, also Li, fig. o). A similar effect is i)roduced by mutilation of 

 the frog. The frog is intended by nature to sustain a large portion of 

 the weight of the animal. 



952. The Frog. 



The Frog (c, fig. 1, also c, fig. G, Plate 19), except in disease, needs 

 only the same treatment as the sole, namely, to be let alone. The fro*^' 

 is an elastic pad placed on the back of the foot. It exfoliates in flakes 

 in due time in much the same way as the sole. Therefore it does not 

 need to be pared. The structural reasons against paring it are much the 

 same as those detailed above in regard to the sole. 



There is, however, another reason against paring it. Unlike the solo 

 the frog is prominent and convex. It is therefore obviously intended by 

 nature for pressure and friction. Under the influence of its natural use 

 viz. jircssure and friction, it Avill thrive, develop, and become strong. 

 ^^'ithout pressure and friction, it will shrink up and dwindle away and 



