392 DISEASES OF THE HOESE. 



scratches, and navicular disease predispose to thrush, while by some a 

 constitutional tendency is believed to exist among certain animals 

 which otherwise present a perfect frog. 



Symptoms. — At first there is simply an increased moisture in the 

 cleft of the frog, accompanied by an offensive smell. After a time a 

 considerable discharge takes place — thin, watery, and highly offen- 

 sive, changing gradually to a thicker puriform matter, which rapidly 

 destroys the horn of the frog. Only in old and severe cases is the 

 patient lame and the foot feverish — cases in which the whole frog is 

 involved in the diseased process. 



Treatment. — Thrushes are to be treated by cleanliness, the removal 

 of all exciting causes, and a return of the frog to its normal condition. 

 As a rule, the diseased and ragged portions of horn are to be pared 

 away and the foot poulticed for a day or two with boiled turnips, to 

 which may be added a few drops of carbolic acid or a handful of pow- 

 dered charcoal to destroj^ the offensive smell. The cleft of the frog 

 and the grooves on its edges are then to be cleaned and well filled with 

 dry calomel and the foot dressed with oakum and a roller bandage. 

 If the discharge is profuse, the dressing should be changed daily ; 

 otherwise it may be left on two or three days. Where a constitu- 

 tional taint is supposed to exist, with swelling of the legs, grease, etc., 

 a purgative, followed by dram doses of sulphate of iron, repeated 

 daily, may be prescribed. In cases where the growth of horn seems 

 too slow a Spanish-fly blister applied to the heels is often followed by 

 good residts. Feet in which the disease is readily induced may be 

 protected in the stable with a leather boot. If the thrush is but a 

 sequel to other diseases, a permanent cure may not be possible. 



CANKER. 



Canker of the foot is due to the rapid reproduction of a vegetable 

 parasite. It not only destroys the sole and frog, but, by setting up a 

 chronic inflammation in the deeper tissues, prevents the growth of a 

 healthy horn by Avhich the injury might be repaired. Heavy cart 

 horses are more often affected than those of any other class. 



Causes. — The essential element in the production of canker is the 

 parasite ; consequently the disease may be called contagious. But, as 

 in all other diseases due to specific causes, the seeds of the disorder 

 must find a suitable soil in which to grow before thcA^ are reproduced. 

 It may be said, then, that the conditions which favor the preparation 

 of the tissues for a reception of the seeds of this disease are simply 

 predisposing causes. 



The condition most favorable to the development of canker is 

 dampness — in fact, dampness seems indispensable to the existence and 

 growth of the parasite ; for the disease is rarely, if ever, seen in high, 

 dry districts, and is much more common in rainy than in dry seasons. 

 Filthy stables and muddy roads have been classed among the causes 



