BOG SPAVIN. 297 



chance of the return of the capsule to its original contracted 

 state ; on the contrary, Nature sets about making additions to it in 

 order to guard against the consequences of its dilatation. Attenuated 

 as the capsule has become through its extension, and immediately 

 underneath the skin as its dilated sac now is, there seems danger, 

 not only of this giving way, but of the common integuments even 

 doing so; and therefore is a process of thickening and strengthen- 

 ing set up in the parietes of the sac, by which, in the course of 

 time, they grow from less than an eighth to more than a quarter 

 of an inch in thickness ; nay — as we have witnessed them — to 

 three-quarters of an inch in density. 



In the generality of cases this may be said to be the termination 

 of bog spavin, little else than accumulation of synovia and thick- 

 ening of the dilated sac appearing to take place. This accounts 

 for lameness being unheard-of in bog spavin in its ordinary form. 

 Cases, however, occur in which disease proceeds further — or rather 

 commences; for, so long as ordinary bog spavin continues in statu 

 quo, it can hardly be accounted disease — renewing its attack on 

 the joint, as well in regard to its secretion as to its lining membrane. 

 Mr. Pritchard (in his excellent remarks on the subject in The 

 Veterinarian for January 1849) informs us he has discovered 

 alterations to have taken place in the synovial fluid secreted under 

 such circumstances, as well, in thorough- pin as in bog spavin. 

 "The fluid," he says, "becomes highly charged (first) with cartilage, 

 then with calcareous matter ; and the whole tumour of the hock be- 

 comes converted into ossific substance, of which I have a very large 

 and excellent specimen. The first change in the synovia is in the 

 increase of its albumen. Then cartilage appears, most commonly in 

 the form of cotton threads from one to two inches in length, per- 

 fectly white, resembling fine needle-like worms, floating in the thick 

 deep-coloured synovia. These threads increase in number and size ; 

 then comes the calcareous matter, by which perfect ossification is 

 effected in regular spherical masses ; and in one case, of which I 

 made a particular note, I was surprised at the early period of the 

 disease at which these threads of cartilage appeared, and in con- 

 siderable numbers." 



In respect to the lining membrane of the joint, we have observed 

 VOL, IV. Qq 



