410 DISEASES OF THE HOESE. 



liability to injury. For the same reason horses with excessive knee 

 action are more likely to suffer from this disease than others, concus- 

 sion of the foot and intense pressure on the tendon being common 

 among such horses. 



Besides the above exciting causes must be considered those which 

 predispose to the disease. Most prominent among these is heredity. 

 It may be claimed, however, that an inherited predisposition to navic- 

 ular disease consists not so much in a special susceptibility of the 

 tissues which are involved in the process as in a vice of conformation 

 which, as is well known, is likely to be transmitted from parent to off- 

 spring. The faults of conformation most likely to be followed by the 

 development of navicular disease are an insufficient plantar cushion, 

 a small frog, high heels, excessive knee action, and contracted heels. 

 Finally, the environments of domestication and use, such as dry 

 stables, heavy pulling, bad shoeing, punctured wounds, etc., all have 

 their influence in developing this disease. 



Symjytoms. — In the early stages of navicular disease the symptoms 

 are generally very obscure. "When the disease begins in inflammation 

 of the navicular bone, the animal while at rest points the affected foot 

 a time before any lameness is seen. While at work he apparently 

 travels as well as ever, but when placed in the stable one foot is set 

 out in front of the other, resting on the toe, with fetlock and knee 

 flexed. After a time, if the case is closely watched, the animal takes 

 a few lame steps while at work, but the lameness disappears as sud- 

 denly as it came, and the driver doubts if the animal was really lame 

 at all. Later on the patient has a lame spell which may last during a 

 greater part of the day, but the next morning it is gone ; he leaves the 

 stable all right, but goes lame again during the day. In time he has 

 a severe attack of lameness, which may last for a week or more, when 

 a remission takes place and it may be weeks or months before another 

 attack supervenes. Finally, he becomes constantly lame, and the 

 more he is used the greater the lameness. 



In the lameness from navicular disease the affected leg always takes 

 a short step, and the toe of the foot first strikes the ground; so the 

 shoe is most worn at this point. If the patient is made to move back- 

 ward, the foot is set down with exceeding great care, and the weight 

 rests upon the affected leg but a moment. When exercised he often 

 stumbles, and if the road is rough he may fall on his knees. If he is 

 lame in both feet the gait is stilty, the shoulders seem stiff, and, if 

 made to work, he sweats profusely from intense pain. Early in the 

 development of the disease a careful examination will reveal some 

 increased heat in the heels and frog, particularly after work; as the 

 disease progresses this becomes more marked, until the whole foot is 

 hot to the touch. At the same time there is an increased sensibility 

 of the foot, for the patient flinches from the percussion of a hammer 



