84 OF THE DISEASES 



structure, which then ceases to afford proper pro- 

 tection to the sensitive parts within. But it is 

 from the effect of dirt combined with wet, that 

 the frog suffers most rapidly. The result of the 

 disease set up in the sensitive structure is an 

 increased and unhealthy secretion, which issues 

 through the cleft and through fistulous openings in 

 other parts of the frog. 



Disease in the frog is also readily produced by 

 paring, contraction, or any other causes which 

 bring it into disuse. 



Work, wear, and pressure, are natural to the 

 frog, and essential to its health and development. 

 If, however, by being constantly pared away at 

 each shoeing the frog is deprived of pressure and 

 wear, it soon becomes unhealthy and diseased. 

 In feet, affected with navicular disease, a similar 

 effect after a time is produced on the frog, because 

 the horse, on account of the disease, the seat of 

 which is immediately above the frog, " saves " as 

 much as possible that portion of his foot, and treads 

 on his toes. It is singular, however, to remark 

 that this effect on the frog is often not found in 

 the earlier stages of navicular disease. Again, in 

 contracted feet, the sole is generally so much re- 

 cessed that the frog hardly ever comes to the 

 ground, and hence, again, from want of use it 

 becomes diseased. 



If the frog be pared, a further cause of disease 



