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their conclusions from false premises believing them to be true. 

 They have fallen into the very common error of reasoning from 

 the particular to the general and mistaking exceptional and 

 abnormal conditions for those of a natural and healthy stand- 

 ard. 



Here is the argument as they present it : " The existence of 

 a crack in the quarter is the invariable result of expansion ; 

 then if the result of expansion, it cannot be caused by contrac- 

 tion ; therefore there is no such thing as contraction." This 

 is the gist of the so-called argument against contraction in any 

 sense as commo?dy understood. 



THE TRUE RATIONALE OF QUARTER-CRACK. 



In stating what I consider to be the true etiology and path- 

 ology of quarter-crack, I shall be at the same time exposing 

 the illusive character of this argument. I regard the sequence 

 of causes as follows : 



Weakening the sole generally has the effect of weakening the 

 lateral support of the quarters, which facilitates their wiring in 

 at the lower circumferent margin, posterior to the wings of the 

 coffin-bone. This wiring in diminishes the area of frog-pressure 

 at the lower circumferent margin, but increases it at the upper 

 margin, from whence the quarter-crack invariably starts. 



This "wiring in," "falling in," or "contraction" of the 

 quarters at this part, produces a gradual approximation and 

 elevation of the margins of the great sole fissure, and therefore 

 the whole of the frog tissues, sensitive and insensitive, become 

 correspondingly elevated. The frog-tissues thus elevated 

 creates a depressive force at the anterior portion of the sole, 

 which results in preternatural expansion around the region of 

 the toe and under certain favoring conditions the wall at the 

 toe splits, and we have the condition called toe-crack. 



CENTRES OF ROTATION, OR MOTION. 



The view which dominates my own mind, and which I find 

 it more easy to demonstrate upon the foot of the horse than to 

 convey either in written or spoken language, has reference to 



