DISEASES. 647 



haps more the genesis of the disease than dryness alone. A foot 

 too much impregnated with dampness, which is afterward left to 

 the air, becomes harder than a normal one placed ia the same con- 

 ditions. It retracts easier, also. It is probable that the water, in 

 softening the superficial layers of the wall, also renders the evajD- 

 oration of the hquids of its deep parts more active. In the ordi- 

 nary condition of the foot, the evaporation is diminished by the 

 impermeability of the external hoof, which it owes to its density ; 

 but where this hoof is softened by maceration, its fibres, partly 

 disintegrated by the dissolution of the glutinous substance which 

 keeps them as a compact mass, allow the air to penetrate in their 

 interspaces ; air which dries them to a certain depth ; hence a 

 groportionate movement of retraction of the entire hoof upon 

 itself. This evil effect of an excess of moisture explains how it is 

 that poultices or other moist appHcations which horse attendants 

 abuse so frequently, may give rise to results entirely opposite to 

 the one in view, and why the hoof becomes dry and brittle, if not 

 contracted. These topical applications take off from the cortical 

 layer of the foot its protecting varnish, and expose it to lose its 

 water of growth. 



Some of the practices in shoeing contribute also to the dessi- 

 cation of the hoof ; such is priacipally that which consists ia rasp- 

 ing the waU from the coronary band to the plantar border : as 

 also the too long continued contact of a hot shoe with the foot. 



Shoeing itself promotes the same result, as, protected by a 

 shoe, the foot no longer wears normally and grows beyond nor- 

 mal limits. The mass of hoof which, in the process of growth, 

 has gone beyond the inferior limits of the podophyllous fissures, is 

 no longer in contact vnth the living parts beneath, and they cease 

 to be impregnated by the fliiids which are thus constantly allowed 

 to evaporate. It then dries up by evaporation and become hard, 

 and retracts upon itself in such a manner that the circumference 

 of the foot in the lateral diameter diminishes more or less, espec- 

 ally posteriorly, and thus forces the incurvations of the sole and 

 of the bars (H. Bouley). If a horse remains shod for several 

 months without having his feet trimmed and pared by the black- 

 smith, these are seen contracting by degrees, as they increase in 

 length, and soon assume the aspect of hoof-bound. 



But these are not the only effects of shoeing in the etiology of 

 contraction. On the contrary, this practice is the most common 



