376 . SOLUTIONS OF CONTINUITY IN THE HOEN. 



actual lameness. The central portion of the frog first dis- 

 appears ; and as a result of the unopposed pressure of the wall 

 the limbs next approach and fill up the previously existing 

 cleft, a condition which renders it difficult to keep the space 

 clean. At the same time, the discharge gradually attacks the 

 horny bulbs and may lead to a similar process in the periople. 

 This is followed by the formation of rings in the superficial 

 horny sheath of the wall. The rings can be distinguished 

 from those of the deeper sheath both by their appearance 

 and course. They usually consist of slight elevations, which 

 approach in front and towards the upper part of the foot, 

 where they may end or again may take an irregular course 

 backwards, extending as far as the opposite half of the 

 wall. They always cross the rings of the deeper sheath ; 

 indeed, when thrush has existed for a long time, they some- 

 times cross one another. This peculiar ring formation, which 

 is almost pathognomonic of thrush, .shows that the disease has 

 existed for at least several months. 



Thrush results chiefly from want of cleanliness, insufficient 

 exercise, and faulty shoeing. If for a long time the frog is 

 prevented touching the ground by excessive trimming, or by the 

 use of unsuitable shoes, it either atrophies or thrush develops. 

 Prolonged rest, however, without any fault in shoeing, may 

 produce the disease. It has been suggested that thrush is due 

 to inflammation of the sudoriparous glands of the frog. 



Prognosis. — The views held as to the significance of thrush 

 are unusually varied. Some regard it as a very trifling 

 disease, which may continue for years without any particular 

 ill consequence, or even as a benign condition not to be inter- 

 fered with. 



If thrush in itself is not of much importance, it often leads, 

 however, to much more serious conditions. It weakens the 

 framework of the hoof, and in flat feet favours the advent of 

 contraction. It may interfere with the animal's use, and even 

 when not actually producing lameness, it causes the stride ta 

 be shortened and diminishes freedom of movement. When 

 affecting one side of the frog, it is apt to lead to unilateral 

 contraction and obliquity of the hoo.f. In addition, it has 

 been held responsible for the production of corns, sandcracks, 

 and even canker. 



