Williams, Fisher, and Udall: The Spavin Group. 33 
the special study of osteo-porosis, but to no avail. If that one 
malady, if it be separable from the others, could be definitely 
described and differentiated from other diseases, it would be 
a great help. In the present state of our knowledge, we can 
only say that spavin and its allies appears frequently as a mani- 
festation of this disease or group of diseases. 
A Rareryine Ostitis, Nor AT Present IDENTIFIABLE WITH 
EITHER OF THE PrEcEDING. We regret possibly adding to the 
confusion by calling special attention to a form of disease ex- 
Pressing itself preéminently as spavin or its allies. 
It occurs in the form of a rarefying ostitis affecting most, 
visibly the short bones like the phalanges, navicular and sesa- 
moids, and the lesser bones of the tarsus and carpus, producing 
the characteristic lesions already described. The indefiniteness 
‘of the preceding affections renders it difficult to place this one. 
It presumably belongs among the three, but whether to call 
it osteo-malacie, rhachitis, or osteo-porosis, we are at a loss 
to state. Either name might well be applied etymologically, 
since it affects the spinal column, and hence may be called 
thachitis; the bone is softened, rendering the term osteo- 
malacie appropriate, and the bone is abnormally porous, which 
permits the designation of osteo-porosis. In the area of our 
chief observations of this disease, the neighborhood of Ithaca,. 
New York, the affection is very common, has no limitations 
as to age, sex, or breed. It appears frequently in the form 
of ringbones and spavins in foals of three or four months, and 
is very common during the first winter of the foal’s life. It is 
not at all rare to see such a foal with two spavins and four 
ringbones ; with adult horses, on the other hand, the exostoses 
are usually not so symmetrical and universal. In some cases 
there is but one discoverable exostosis during life, and between 
this and cases where a sound joint does not seem to exist, but 
where the lesions are only discoverable upon post-mortem 
examination after cleaning the bones, there is every gradation. 
In severe cases there are constitutional disturbances of a 
marked character expressed by a general appearance of bad 
health, and, among other things, an excess of phosphates in 
the urine? 
In the region mentioned, typical osteo-porosis, with the 
enormous bulging of the facial and cranial bones, is wholly 
unknown. In nine years there has not been a case typical of 
