CANKEE. 171 



which is a question that has not yet been settled. Thrush, differ- 

 iug from canker, can often be cured by merely keeping the frog 

 dry, and by putting pressure on it by lowering the wall, especially 

 at the heels. Similarly, ordinary cracked heels may be cured by 

 attention to healthy conditions ; although recovery from grease 

 is seldom, if ever, possible, without special treatment. The 

 peculiar liability of the frog to become the first point of attack 

 of canker, appears to be due to its giving, particularly when it is 

 affected by thrush, less protection to the invaded membrane than 

 the sole would afford. Also, the influences (such as wet and dirt) 

 which predispose to canker, are the very ones which are mainly 

 concerned in the production of thrush. Injury would naturally be 

 liable to expose the secreting membrane to infection or irritation. 

 In cases of thrush, the secreting membrane of the frog is exposed 

 to external infection, injury, or irritation, through the opening in 

 the cleft of the frog, which, in health, is merely a shallow de- 

 pression in the frog. Canker may be seen without the fissured 

 condition of the cleft of the frog which is a characteristic of thrush. 

 From the foregoing facts, I think it most improbable that thrush, 

 however much neglected or aggravated, could, of itself, set up 

 canker; although, as we have seen, it is a strong predisposing 

 cause. In some cases, caniker appears to be due to the ex- 

 tension of the inflammation of " greasy " heels, on account of the 

 membrane which is the seat of canker, being continuous with the 

 skin of the pastern. Correct treatment evidently consists in the 

 removal or destruction of all involved tissue; in the application 

 of antiseptics ; in pressure ; and in the protection of the exposed 

 surface from further infection, until that duty can be taken by a 

 new growth of healthy horn. 



TREATMENT.— Mr. Malcolm, F.R.C.V.S., in reviving the treat- 

 ment of canker by the use of the hot iron, which has been 

 employed, not very successfully, by Prevost, Hurtel d'Arboval 

 and others, has introduced new modifications that have been 

 attended with excellent results. He advises (" Journal of 

 Comparative Pathology," March, 1891) that after the horse 

 has been cast, the whole of the implicated horn should be 

 removed with the drawing knife, and that the entire dis- 

 eased secreting surface should be thoroughly cauterised with the 

 hot iron, which is an " aid of immense value in diagnosis. Applied 

 to the thinned horn or the secreting surface, it unmistakably demon- 

 strates the presence or absence of canker. Healthy tissue chars 

 black : cankered tissue, on the contrary, bubbles up white under 

 the hot iron, and presents an appearance not unlike toasted cheese. 

 Although this test is certain for hora thinned to the quick, it is not 



