38 Williams, Fisher, and Udall: The Spavin Group. 
The part, consequently, which concussion plays in the locali- 
zation of the disease, is probably considerable and of the same 
general character as the influence of strain; that is, the part 
is damaged by the concussion, not because the latter is extraor- 
dinary, but as a result of decreased power of resistance in the 
bone as a result of disease. 
The breed of the animal fixes in a measure the character of 
the labor and the two factors acting through the preceding causes, 
apparently influence the localization. Draft breeds are rarely 
kept confined in the standing position so long as smaller horses, 
nor are they kept confined in stables for so long periods, their 
work being more constant. They do not suffer so much from 
navicular disease, probably because this bone is not subjected 
to so much abnormal, continued compression. But here we 
are frequently deceived by navicular disease being hidden be- 
neath ringbone or sidebones, so that it is not diagnosed. Per- 
haps another reason acts in these cases. Draft horses have flat 
feet, and if the navicular bones become painful from disease 
and the horse attempts to relieve the compression, the pedal. 
bone may move backward and downward and sinking of the. 
os pedis result instead of, or along with the navicular disease. 
On the other hand, strain and concussion play a more 
important part in the draft horse, and we see comparatively 
more frequently those forms of the disease most readily charge- 
able to these factors. - 
The conformation of the limb by which the compression, 
strain, or concussion is modified in a given part influences the 
localization of the disease. If a hock be faulty and other articu- 
lations good, we should expect that fact to tend to determine 
the disease assuming the character of spavin in preference to 
other forms. 
THE CAUSES OF LAMENESS. 
This group of diseases is so often accompanied by lameness 
and so frequently not that it is desirable to know upon what 
conditions it depends, since upon our judgment in this matter 
rests the value of our opinion as to the prognosis and the prob- 
able usefulness of the patient. 
So far as we know, when the subchondral bone has been 
removed and the articular cartilage has dropped into the cavity, 
causing the familiar erosions, the animal can never again go 
