LAMENESS: ITS CAUSES AND TREATMENT. 327 
On the occurrence of the injury an effusion of blood takes place be- 
tween the ends of the bone. The coagulation of the fluid soon fol-. 
lows, and this, after a few days, undergoes absorption. There is 
then an excess of inflammation in the surrounding structure, which 
soon spreads to the bony tissue, when a true ostitis is established, 
and the compact tissue of the bone becomes the seat of a new vascular 
organization, and of a certain exudation of plastic lymph, appearing 
between the periosteum and the external surface of the bone, as well 
as on the inner side of the medullary cavity. After a few days the 
ends of the bone thus surrounded by this exudate become involved 
in it, and the lymph, becoming vascular, is soon transformed into 
cartilaginous, and in due time into bony, tissue. 
Thus the time required for the consolidation of the fractured seg- 
ments is divisible into two distinct periods. In the first they are sur- 
rounded by an external bony ring, and the medullary cavity is closed 
by a bony plug or stopper, constituting the period of the provisional 
callus. This is followed by the period of permanent callus, during 
which the process of converting the cartilaginous into the osseous 
form is going forward. 
The restorative process is sooner completed in the carnivorous than 
in the herbivorous tribes. In the former the temporary callus may 
attain sufficient fineness of consistency for the careful use of the limb 
within four weeks, but with the latter a period of from six weeks to 
two months is not too long to allow before removing the supporting 
apparatus from the limb. 
This, in general terms, represents the fact when the resources of 
nature have not been thwarted by untoward accidents, such as a want 
of vigor in the constitution of the patient or a lack of skill on the 
part of the practitioner, and especially. when, from any cause, the 
bony fragments have not been kept in a state of perfect immobility 
and the constant friction has prevented the osseous union of the two 
portions. Failures and misfortunes are always more than possible, 
and instead of a solid and practicable bony union the sequel of the 
accident is sometimes a false joint, composed of mere flexible carti- 
lage, a poor pseudarthrosis. The explanation of this appears to be 
that, first, the sharp edges of the ends of the bone disappear by 
becoming rounded at their extremities by friction and polishing 
against each other. Then follows an exudation of a plastic nature 
which becomes transformed into a cartilaginous layer of a rough, 
articular aspect. In this bony nuclei soon appear, and the lymph 
secreted between the segments thus transformed, instead of becoming 
truly ossified, is changed into a sort of fibrocartilaginous pouch, or 
capsular sac, in which a somewhat albuminous secretion, or pseudo- 
synovia, permits the movement to take place. Most commonly, how- 
ever, in our animals, the union of the bony fragments is obtained 
