28 THE ART OF HORSE-SHOEING. 



delicate to be trustworthy. Experimentalists in Ger- 

 many and in this countr}^ have recently used an appar- 

 atus by which the slightest variations are detected by 

 electrical contact, and the results are very interesting. 

 These experiments show that in a well-formed, healthy 

 foot the hoof, throughout its posterior two-thirds, does 

 expand to j)ressure, and perhaps that the arch of the 

 sole is slightly flattened. This expansion is, however, 

 comparatively slight — about equal to the thickness of a 

 sheet of writing paper — and may practically be disre- 

 garded in considering the best methods of shoeing sound 

 feet. 



One result of these experiments is to show what an 

 important part the frog plays in the foot, and also how 

 the action of one part depends upon the conditions of 

 others. Yriien the frog rests firmly on the ground and 

 weight is placed upon the foot, expansion occurs, espe- 

 cially at the upper or coronary border of the hoof. 

 When the frog does not touch the ground and weight is 

 imposed upon the foot, contraction occurs. The expla- 

 nation of this difference seems to be as follows. When 

 weight is placed upon a foot, the coronet bone is 

 depressed upon the soft mass of the frog-pad. With a 

 sound frog taking a bearing upon the ground, the frog- 

 pad cannot descend, and the compression to which it is 

 therefore submitted causes it to bulge laterally and so 

 expand the back of the foot. When the frog does not 

 reach the ground, and weight is placed upon the frog- 

 pad, there is nothing to prevent it yielding downwards, 

 and in so doing, the fibrous bands connecting together 

 the two lateral cartilages of the foot are depressed and 

 the cartilages drawn together; hence the contra.ction of 

 the foot. No better illustration could be given of the 

 unity of all parts of the foot, and how one or many parts 

 may suffer if the structure or function of one be defective. 



There is one more movement of the hoof which is 

 possible and which must be referred to, as it has been 

 luade the basis of a grave error in shoeing. I have said 

 the back part of the foot is elastic and yielding. If you 

 ■examine a shoe, so applied to a foot that an inch or more 



