Williams, Fisher, and Udall: The Spavin Group. 39 
sound unless the articulation or bursa has become obliterated 
through anchylosis or the sensation has been surgically de- 
stroyed. But this lesion is not essential to the production of 
lameness. In some cases we have all the cardinal symptoms of 
navicular disease or spavin without externally visible changes 
in structure, such as exostosis, synovitis, or periostitis, and their 
prompt recovery forces us to conclude either that an error in 
diagnosis has been made or that the pathologic condition was 
such as to admit of prompt resolution. We do not believe that 
a prompt recovery from what appears as typical navicular lame- 
ness is conclusive evidence of diagnostic error, but hold it not 
only to be possible, but of not very infrequent occurrence. So 
with other forms of the disease, and we must find other explana- 
tion for the pain. We have observed well-marked cases of 
general soreness with typical symptoms of navicular disease 
or other member of the group which responded quickly to treat- 
ment, and in which neither erosions, exostoses, periostitis, nor 
synovitis could be recognized or their presence in a serious. 
degree suspected, and we were forced to the conclusion that 
the intra-osseous pain resulting from the pathologic changes 
going on is responsible for the lameness. In one case of very 
severe lameness, a careful autopsy failed to reveal superficial 
lesions in keeping with the pain, and it could only be attributed 
to intra-osseous pain resulting from the ostitis. In Figs. II and 
III at B the inflammation would seem sufficient to induce lame- 
ness without the lesions at C. 
In many cases, especially in ringbone, there is severe lame- 
. ness without good proof of erosions, and the exostoses are so 
situated as to not interfere materially with the movements of 
the articulation. It is impossible to determine here whether the 
pain is caused by the exostoses or by the intrasosseous changes; 
probably it should be referred to both, but after the subsidence 
of the active inflammation, we observe repeatedly that exostosis 
does not cause pain. Whether within the original bone, within 
the new formed bone, or in the periosteum, the lameness must 
be due to inflammatory processes still at work. 
The synovitis in itself probably causes lameness sometimes, 
though we do not find cases, except perhaps in navicular disease, 
where manipulation can induce pain. With the common ten-— 
dency toward anchylosis, we must anticipate frequent interrup- 
tions in the process; two bones will become partially anchy- 
