142 THE PRACTICE OF VETERINARY MEDICINE. 



readily be understood that the presence of any foreign sub- 

 stance, as a melanotic tumour, for instance, pressing upon 

 the nerve, or in any way interfering with the nerve, would 

 be sufficient to cause it to perform its function in an im- 

 proper manner. Some think it is due to stimulation of the 

 nerve centres, while others consider it to be caused by 

 irregular nervous influence due to reflex action, emanating 

 from a diseased hock or joint. Want of power, due to 

 paralysis of the opposing muscles, cramp of the flexor meta- 

 tarsi, rheumatic affection of the muscles, shortening of the 

 flexors of the hock, and a thousand other so-called explana- 

 tions have been given. The latest is the theory of Ginther, 

 who considers that it is due to a shrinking of the fascia of 

 the limb, and, as proof, he claims to have cured the disease 

 by cutting through the fascia. This theory, however, is 

 scarcely tenable. It is a difficult disease to understand. 



Symptoms. — The disease is influenced and aggravated by 

 cold. Some cases have come under observation that were 

 very badly affected during the winter, while in summer the 

 condition was scarcely noticeable. The peculiar action of 

 the hind limbs is better seen when the animal moves for- 

 ward. The limb is jerked, and it is plain to anyone that 

 the action is a wholly involuntary one. In some cases the 

 animal may move quite a distance before jerking the leg 

 up. Again, some animals must be turned, first to one side 

 then the other, backed, and led forward, in fact, put 

 through every conceivable movement, before the tell-tale 

 jerking of the limb can be discerned. The practitioner 

 cannot be too careful or energetic in his endeavours to dis- 

 cover this defect when examining a horse as to soundness. 

 In some cases it is better noticed when the animal trots 

 than at any other time. In examining the animal, walk 

 liim quietly along, then trot him ; after Mhich, turn him 

 first one way and then the other, back him forcibly, and 



