CAUSES OF 'THRUSH.' 63 



1 must repeat that the structure of the hoof im- 

 peratively demands that the wall, frog, and sole shall 

 each be called into play, each be worn away natu- 

 rally, and each be perpetually reproduced. 



Although intended to benefit the horse, the or- 

 dinary shoe does it a serious injury in frustrating 

 each of these requirements. As the iron of the shoe 

 is interposed between the wall and the ground, the 

 horn of the Avail cannot be worn away, especially in 

 front, where the friction is greatest, and where the 

 horn grows fastest. As the frog is cut away, it 

 cannot take the weight of the horse as it ought to do, 

 and therefore communicates no movement either to 

 the sole or the lamina? of the wall, and so there is 

 /none of the incessant expansion and contraction 

 which the hoof requires. 



I need hardly explain that all repair of organic 

 waste is effected by means of blood, and that the 

 supply of blood is proportioned to the amount of 

 work to be done by it. 



Now. if the skin be stripped off the shank of the 

 horse, the bone will be seen surrounded with a series 

 of very large arteries and veins, intended to carry 

 blood into and from the hoof, so as to supply the 

 continual waste of the horn, the arteries and veins 

 exactly balancing each other. But when that waste 

 is checked, the balance of circulation is destroyed. 



