646 OPERATIONS ON" THE FOOT. 



V. Etiology. — Hoof-bound, says H. Bouley, is not a simple 

 fact, produced by a unique cause acting always in the same man- 

 ner : it is, on the contrary, a very complex one, to the production 

 of which a great number of causes of various character and inten- 

 sity contribute with simultaneous or successive effects. 



The hygrometic condition of the horny substance is a principal 

 feature in the etiology of the disease. It is when the hoof loses 

 by evaporation the moisture which it should contain that it con- 

 tracts as all organic substances do, and its flexibility returns when 

 by sufficiently long immersion in a Hquid, the moisture it has lost 

 is recovered. Observation proves that this disease often finds the 

 conditions of its presence ia circumstances which induce dryness 

 ia the part. In stich cases the foot has the property of retracting, 

 to an extreme degree, especially toward its posterior extremity, 

 where the frog is situated, constituted as it is of a softer and 

 more depressible substance than that of the wall. The same ^jhe- 

 nomena takes place in the living structure that is observed upon 

 the hoofs of dead feet ; a phenomenon which cannot even be pre- 

 vented by filling their cavity with plaster. During life the hoof is 

 constantly permeated by a current of fluids which penetrate it 

 from its depth to the surface. It is the serous food that the hoof 

 is continually absorbing by the hygroscopic properties common in 

 Uving tissues, which counterbalance the tendency of the foot to 

 retract upon itseK and keep it in the dimensions required for the 

 perfect reception of the parts it covers. So long as the equilib- 

 rium is preserved between the loss of this fluid by evaporation 

 and its renewal through the perspiration of the keratogenous 

 apparatus, the hoof preserves its physiological form ; but if this 

 equilibrium is destroyed by an excess of the loss, then the condi- 

 tion occiu's for the retraction of the hoof and the infliction upon 

 the parts underneath of an excessive and painful pressure. 



This explains why, as proved by observation, lameness in 

 general and that of contracted heels especially, is more frequent 

 in warm than in moist seasons. Long standing in the stable is 

 also an efficient producing cause. The feet become dry upon a 

 constantly dry bedding, and here also the influence of inaction 

 must be taken into account. The disease is commonly found in 

 stabulation, but seldom when the animal is in pasture ; and when 

 it has existed it often disappears in the latter circumstances. 



The alternation of dampness and dryness also influences per- 



