300 PARTICULAR LAMENESSES. 



irritation not amounting to actual disease, and may be viewed 

 as a provision of nature to fulfil the purposes ascribed to it by 

 Professor Dick, since it often happens that such hocks remain 

 sound as long as those of a better conformation. They should, 

 however, be looked upon with suspicion, and the practitioner 

 ought at all times to satisfy himself by a severe trial that such 

 hocks are able to bear a reasonable amount of exertion ; that the 

 swelling does not increase after such test, and that the animal 

 be neither stiff nor lame in the slightest degree. 



Inflammation of the true hock-joint may be acute or chronic. 

 In the acute form the lameness is very great, with fever, loss of 

 condition, and inability to put the foot to the ground. It is apt 

 to terminate in ulceration of the articular cartilage and a partial 

 anchylosis of the joint. 



A very constant condition of the joint in the chronic form 

 of bog-spavin, and probably the cause of it, is the gradual con- 

 version of the articular cartilage into calcareous matter — the 

 ivory or porcellaneous deposit. — (See Photo-lithograph, Plate 

 II., Fig. 5.) This condition is associated with the rheumatoid 

 diathesis ; and not only is there a deposit in the cartilage, but 

 also in the synovial fringes, which are converted into hard 

 rounded nodules of calcareous matter. Common inflammation 

 of a joint generally tends to ulceration and anchylosis ; the rheu- 

 matoid, to calcification of the articular cartilage and synovial 

 fringes. 



The sulci of the hock-joint should not be confounded with 

 ulcers. 



When articular cartilage has been calcified, or converted into 

 the ivory-like deposit, it no longer prevents the effects of the 

 friction arising from the movements of the bones upon each 

 other. A careful examination of Photo-lithograph, Plate 

 II., Figs. 3 and 5, will at once demonstrate this, for it will be 

 seen that the articular heads of the bones are worn down, 

 leaving well-marked, and, in the hock, deep grooves upon 

 them. The polished appearance given to the diseased part 

 was attributed by Professor Dick to the effect of friction on 

 bone otherwise unchanged; but a more careful examination 

 has shown that it is due to an actual formation of a very 

 hard, earthy matter in the Haversian canals, for the purpose 

 of counteracting and limiting the effects of friction, and that 



