CANKER. 171 



frog dry, and 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 treat- 

 ment. The peculiar liability of the frog to become the first 

 point of attack of canker, appears to be due to its giving, 

 particularly when 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 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 depression in the frog. Canker 

 may be seen without the fissured condition of the cleft of the 

 frog, characteristic of thrush. The foregoing facts show how 

 impi'obable it is that thrush, however much neglected or 

 aggravated, could, of itself, set up canker ; although it is a strong 

 predisposing cause. In some cases, canker appears to be due to 

 the extension 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 Com- 

 parative Pathology," March, 1891) that after the horse has been 

 oast, the whole of the implicated horn should be removed with 

 the drawing knife, and the entire diseased secreting surface 

 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 demonstrates 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 horn thinned to the quick, it is not to be 

 relied upon, with thick horn, the outside of which may be practi- 

 cally healthy and char black, while its underlying surface may b^-- 



