CONTRACTION. 463 



being given them tor such changes to be brought about. The 

 action of the frog is but a secondary power in the expansion of 

 the hoof, and when the heels of the hoof are fixed, as they are by 

 those of the shoe, has but feeble agency, unaided by the great ex- 

 pansive effect of the wall of the hoof.of itself in dilating the heels. 



Want of Weight of Body and of Force of Action 

 in the subject may account for lack of expansive power, and 

 so for the predominance of the contractile force. Light horses 

 having slender bodies and going near the ground, with hoofs 

 of a strong and upright and growing fibre, are very subject to 

 contraction from the diminished power there exists in them to 

 expand feet requiring greater force for their expansion ; though, 

 if they should happen to possess high stamping action, this 

 power becomes much augmented during the time they are going. 

 But, even in this case, were it not for the unceasing counter-active 

 effect of the shoe — or, in other words, were the foot set at liberty 

 by being unshod — it would be only under certain circumstances 

 that the operations of nature would be overcome by any such 

 deficiency. Indeed, when horses are shod with tips, so long as 

 the heels are left at liberty, it rarely — never, I believe I may 

 say — happens, that this cause, or even want of pressure to the 

 frog, operates to the production of contraction. Standing tied 

 up in the stable no doubt tends to favour the operation of such 

 causes ; but even here, were they not aided by the imprison- 

 ment of the hoof by the shoe, their influence would be com- 

 paratively feeble. 



The direct Causes of Contraction are neither numerous 

 nor effective when put into competition with those we have 

 mentioned — the indirect : at the same time, when operant with 

 the latter causes or such as tend to prevent expansion, they be- 

 come to a certain degree influential. No agent can be said to 

 be direct save one whose effect is to produce actual contraction. 

 Such influences as operate in occasioning shrinking of the dead 

 hoof or shrivelling of detached horn, such as di'ought, heat, and 

 evaporation, may be expected to take more or less effect upon 

 the hving as well as the dead hoof, if not in their ordinary form, 

 at least when applied in any inordinate degree. Heat has this 



