246 LAMENESS. 



exostoses on a nerve, and to paralysis of the muscles antago- 

 nistic to those affected with the spasm. In one case which fell 

 under my notice, melanosis within the spinal canal was the cause 

 of chorea ; but the spasm (clonic, or rapidly alternating contrac- 

 tions and relaxations) of chorea is not a phenomenon of persis- 

 tent spinal irritation, while tonic spasm is a mark of such a 

 condition. 



Chorea may be divided into partial, as in stringhalt in the 

 horse, and general, as seen occasionally in dogs. 



Stringhalt may be defined to be an involuntary convulsive 

 motion of the muscles, generally those of one or both hind legs, 

 but occasionally it is seen in the fore legs also. 



The limb or limbs affected are convulsively elevated from 

 the ground, and brought down again with more than natural 

 force. It is not always to be noticed at every step the horse 

 takes. He may go several paces, as many as twenty, without 

 exhibiting any signs of stringhalt ; then, aU at once, the limb 

 or limbs will be suddenly elevated from the ground with a 

 peculiarly sharp sudden jerk. It is necessary sometimes to turn 

 the animal round from right to left, and from left to right, in 

 order to make him show any signs of stringhalt, the symptoms 

 of the disease being exhibited as he turns one way only. It is 

 generally developed slowly, but I have seen very aggravated 

 cases come on in one night, and as age advances it always 

 becomes worse. It should be viewed as an unsoundness, and 

 as a cause of depreciation of the animal's value. In two horses 

 which had suffered from very violent stringhalt, the post mortem 

 examination revealed exostoses on the shaft of the ilium, 

 involving the great sciatic nerves. I think its cause is sometimes 

 peripheral, as when a bone-spavin presses upon the nerves of 

 the hock. The stringhalt then is due to reflex nervous action. 



In grey horses, stringhalt is occasionally due to a deposition 

 of melanotic material in the sheath of the great crural nerves. I 

 am inclined to the opinion tliat chronic stringhalt, or that form of 

 it not dependent on rlieumatism, arises from a congested condition 

 of the nerves and their sheaths, and that there is always a tendency 

 to the occurrence of neuritis from causes that would otherwise 

 have no effect upon the nervous system. This view is supported 

 by the fact that injuries to the feet, or any part of the limbs 

 affected with stringhalt, are very prone to be succeeded by increase 

 of the spasm, by much nervous excitement, and bv tetanus. 



