NAVICULAR DISEASE. 
641 
In the later stages the muscular tissue of the limb atrophies more 
or less, depending on the degree of lameness (atrophy from want of 
function). 
Since the discovery of cocain a valuable aid in diagnosis has been 
afforded. By injecting a few minims of a 5 per cent, solution of cocain 
over the course of the plantar nerves, temporary anaesthesia of the lower 
portions of the limb is produced ; disappearance of lameness under these 
circumstances renders it probable that the seat of disease is in or about 
the foot. 
The first stages of the disease generally pass unnoticed, until the 
gradual increase of lameness draws attention to them. The lameness 
may disappear with long rest, but always returns after hard work. 
Weeks and months pass, until at last it becomes necessary either to get 
rid of the animal or to perform neurectomy. Becovery is rare, and 
supposeci cures mostly result from faulty diagnosis or from mistaking 
remission for recovery, as shown by the above-reported opinions of the 
older English authors, who put the average of recoveries at 90 per 
cent. Bracy Clark, an able observer, assesses them, on the other hand, at 
1 in 16. From the nature of the disease, recovery must be rare, and 
can only occur during the first stages, i.e., while the disease is confined to 
the bursa of the flexor tendon. Prognosis is most favourable when, on 
account of the sudden onset of lameness, there is a probability that 
inflammation is confined to the tendon and bursa, and that the flexor 
surface of the navicular bone is still intact. But when atrophy of 
muscle or hoof has set in, improvement is not to be expected. Excep¬ 
tional cases are seen, however, where recovery, or at least cessation of 
lameness, is produced by adhesion of the perforans tendon to the 
navicular bone. Gerke confirmed this by a post-mortem two years 
after the disappearance of lameness. Peters had a similar case, but 
such a termination is very exceptional. 
Neurectomy, often resorted to to remove sensation, is apt to be 
followed by rupture of the perforans tendon. The tendon becomes more 
and more abraded by the rough surface of the navicular bone, until at 
last, in a moment of excessive strain, it suddenly tears through, leaving 
the horse completely useless. Temporary improvement following long 
rest must not be mistaken for cure. 
The disease is not nearly so common as was formerly believed, and is 
often confused with diseases of the hoof and other lamenesses. Errors are 
easy, unless plenty of time is given to the examination, and diagnosis 
sometimes proves difficult, even to the most practised. 
Differential Diagnosis. 
The condition may be mistaken for— 
(1) Contracted sole. The form of the hoof, the strongly concave sole, 
V.S. T T 
