AS TO SOUNDNESS. 81 
LECTURE XI. 
NAVICULAR DISEASE. 
GENTLEMEN,—We now come to the subject of navi- 
cular disease, vulgarly called ‘‘ groggy lameness.” 
This is no place for much pathological reasoning, but 
as very different explanations have been given as to both 
the causes and nature of the affection, I feel bound 
to say a few words about it, although I would like alto- 
gether to evade the question. And it would be not only 
possible but reasonable for me to do so were the affec- 
tion always apparent, as quittor or canker is appareut ; 
but it is in many cases so concealed that we can only 
arrive at the conclusion that we have navicular disease 
by a process of exclusion, that is to say, when we find a 
case of lameness of the fore extremity, and we fail to find 
any physical defect we conclude that it must be 
navicular disease which is causing the lameness, or, in 
other words, we have to guide us, 
Negative Signs and Symptoms. 
Before going any further I will trespass on your time 
by defining the difference —the vast difference—between 
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