220 OPERATIONS ON BONES. 



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 fractiu'ed 

 segments is divisible into two distinct periods. In the first they 

 are surrounded by an external bony ring, and the medullary ca\dty 

 is closed by a bony plug or stopper, constituting the joeriod of the 

 provisional callus. This is followed by the period of perinanent 

 callus, during which the process is going forward of converting 

 the cartilaginous into the osseous form. 



The restorative process is sooner completed in the carnivorous 

 than in the herbivorous tribes. In the former the temporary callus 

 may attain sufficient firmness or consistency for the careful use 

 of the limb within four weeks, but with the latter a period of from 

 six w^eeks to two months is not too long to allow before removing 

 the supporting apparatus from the Hmb. 



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 esjDecially 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, com- 

 posed of mere flexible cartilage, a -poor 2^seudo-arthrosis. The ex- 

 planation of this appears to be that, first, the sharp edges of the 

 ends of the bone disappear by becoming rounded at their extrem- 

 ities, by friction and polishing against each other. Then follows 

 an exvidation 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 fibi'O-cartilaginous pouch or capsular sac, in which 

 a somewhat albuminous secretion, or pseudo-synovia, permits the 

 movement to take place. Most commonly, however, in our 

 animals, the union of the bony fi-agments is obtained wholly 

 through the medium of a layer of fibrous tissue, and it is because 



