620 OPEEATIONS ON THE FOOT. 



the relative dryness of tlie hoof, which then becomes excessively 

 brittle. We have seen the conditions in which the hoof loses its 

 natural flexibility, and shall here only state that alternate changes 

 from dampness to dryness have as much influence as the drjTiess 

 alone. Cracks are more frequent in animals working along damp 

 than in those j^ulling in dry and stony roads. They are common 

 in animals which after being kept in pastures are placed in good 

 paved stables, with dry bedding. It is principally in these condi- 

 tions we find the quarter-crack. During some seasons, while a 

 term of dryness follows continued wet weather, the conditions are 

 favorable to their formation, and they often assume an epizootic 

 form. Emigration to dry cUmates is a frequent cause, by produc- 

 ing the contraction of the ungueal structure. This last cu'cum- 

 stance explains why cracks are more common in army horses, 

 which are called to go on long journeys during the warm days of 

 summer But if the European horse taken to Africa suffers less 

 from the disease, a similar result occurs to the African horse when 

 brought to our climate. The Arabian horse readily contracts 

 quarter-cracks in our stables, and with our shoeing. Animals with 

 small feet, or with hard and thick hoofs, have a natural predispo- 

 sition, which is also found in Hungarian, Kussian or Tartar ani- 

 mals. Feet excessively large are also easily affected with the 

 disease, esj)ecially those which have canker or grease. 



Unskilful shoeing may predispose to cracks, and this is princi- 

 l^ally the case if the wall is thinned or rasped down too much ; 

 the same result is obtained from shoes which are too wide or too 

 heavy, or which are kept on by too heavy nails. 



Feet with toes turned outward are predisposed to it, as in 

 these the weight of the body rests more on the internal quarter, 

 which being thinner than the external, give way the easiest. Con- 

 tracted feet are subject to it. Quittor, suppurative corns, and 

 some other diseases, are also predisposing causes. Among occa- 

 sional or accidental causes may be mentioned ti'aumatism, contu- 

 sions of the foot and blows during work. The service of heavy 

 trucking for heavy horses exposes the hind feet to toe-crack, 

 especially if the pulling is done in going up hill or on slippery 

 pavements; mules' feet are very subject to it, and heavy falls in 

 jumping and external blows are occasional causes. 



Heredity in cracks has been mentioned. We do not admit 

 this, except so far as it belongs among the predisposing causes 



