THE FOOT. 323 



cells, disposed concentrically around the axis in numerous layers in an 

 imbricated manner. The most superficial of these layers affect a dif- 

 ferent disposition : the cells become perpendicular to the direction of 

 the tube instead of remaining parallel, and in this manner is formed 

 the intertubular horn, a veritable cement substance which agglutinates 

 the hair cylinders to one another. 



c. Color. The horn cells, being epithelial in nature and jformed 

 from the cells of the epidermis of the skin, the hoof assumes a white 

 or black coloration according as the parts which form it are or are not 

 provided with pigment. When the skin of the coronary band is red, 

 the wall is white for an equal extent ; in the opposite case, it remains 

 black. The same considerations are applicable to that of the sole and 

 the frog. , 



d. Consistency. The consistency of the nail is in direct rela- 

 tion with the degree of humidity of the horn, and this humidity is 

 obtained by the foot either from the surrounding atmosphere or from 

 its own tissues. 



The temperature of the soil, the quality of the pasture, the hygro- 

 metric state of the air, the season of the year, the nature of the 

 climate, are so many causes whose influence is evident and which it is 

 needless to dwell upon. 



Likewise, the horn becomes more supple and softer as it is exam- 

 ined closer to the living tissues ; it is, on the contrary, more resisting, 

 brittle, and difficult to cut as it is more distant. The superficial parts 

 of the frog, the sole, and the wall, the inferior border of the latter, 

 are always excessively dry compared to the deeper parts of these 

 structures. 



These diverse conditions of the hoof, when existing in extremes, 

 offer serious evils from the double point of view of the preservation 

 of the foot and the use of the animal. We will revert to this in the 

 chapter on defects. 



Growth and Wear of the Hoof. New layers of horn are 

 incessantly secreted at the level of the villous papillae of the kerato- 

 genous apparatus, pushing down the older layers to repair the loss 

 occasioned by use. It is clear that each portion of the hoof grows 

 according to the direction of its own fibres : the wall in its height, the 

 sole and the frog in the sense of their thickness. 



This growth is effected slowly. It requires about eight months 

 for the production of a completely new hoof. All loss of substance to 

 the wall is therefore reproduced very slowly ; whence the lesson is 

 taught that we should avoid this loss as much as possible. 



