Williams, Fisher, and Udall: The Spavin Group. 35 
inducing the local lesions as a definite and essential result of 
a traumatic injury, but cannot admit that a mechanical insult 
at one point can induce general histologic lesions throughout 
the bony skeleton and induce serious pathologic changes in_ 
the prinary secretions. It has not yet been determined if a 
spavin, ringbone, or other local lesion ever exists in the active 
or formative stage without a generalized pathologic condition 
of the skeleton and changes in the urine. Granting the exist- 
ence of constitutional disease, the factors which determine the 
localization appear to be largely capable of explanation. 
Referring to the preceding chapter on pathology, it appears 
that the bones most affected are those which we commonly know 
as “short,” and that the chief destruction takes place within 
the lacunze and red marrow, which forms so large a portion of 
these and of the articular ends of the long bones. Thus we 
find the chief expression of the malady in the digits, navicular 
bone, the lesser carpal and tarsal bones, the spinal column, and 
the ribs. But we would not be understood that compact bony 
tissue does not undergo equally important changes in propor- 
tion to its comparative amount of active elements, as is shown 
by theit decreased specific gravity and by their fragility as seen 
in fractures in these cases. The short, spongy bones become 
the chief points of attack because the contain a preponderance 
of the tissues in which the disease works its greatest havoc.. 
We may consider the varieties of mechanical insult under | 
three heads: compression, strain, and concussion, and believe | 
we have related them in approximately their order of impor-~ 
tance. The horse is preéminently an animal of motion, but 
when not in locomotion maintains the standing position rather 
than recumbency in a very remarkable degree in comparison 
with other mammals. Some horses habitually stand while 
sleeping and do not lie down during long periods of time, while 
many horses which are kept in the harness long hours daily 
are compelled to stand a large part of the time, closely tied 
in an uncomfortable position between the thills of a wagon, 
where little opportunity for restful changes of attitude is allowed, 
even the head being fixed by tight reining. This brings con- 
stant pressure to bear upon certain articulations and the bones 
concerned. If we study the anatomical arrangement of the 
navicular bone, we find it being constantly compressed, when- 
ever weight is borne upon the limb, between the unyielding 
