KERATOMA. 



1087 



fistula. Sometimes the tumour presents outwardly a fissure which 

 extends some distance into the substance of the hoof wall, which 

 externally may be intact. 



The activity of secretion in the coronary band is very great ; 

 in the sensitive laminae, on the other hand, it is very small, being 

 only well marked at the upper part of the wall just below the coronary 

 band itself, where the horny laminae originate. But when the sensitive 

 laminae become the seat of chronic irritation, their latent horn- 

 forming power becomes active, and a mass of new horn is produced. 



Horn tumours sometimes start from the coronet, in consequence 

 of treads or other injuries producing chronic inflammation and 

 hyperplasia in the lower papillae of the coronary band. This patho- 

 logical thickening gradually extends downwards towards the ground 

 surface of the foot, and, pressing on sensitive structures, gives rise 

 to chronic lameness. In other cases the sensitive laminae form the 

 points of origin of the tumours. Laminal keratomata are usually 

 confined to the lower portions of the wall, and though they extend 

 upwards towards the coronet, they seldom reach it. 



Keratomata therefore result from chronic irritation, or productive 

 inflammation of the coronary band, or sensitive laminae. Sometimes 

 the condition is followed by superficial suppuration. On the other 

 hand, infective inflammation of the podophyllous membrane may 

 constitute the first phase and be succeeded by a chronic productive 

 process. Horn tumours produce atrophy of the plantar reticulum, 

 sensitive laminae and os pedis. The bone presents a depression or 

 gutter corresponding in form and dimensions to the tumour, and 

 its edges are often studded with asperities or small bony growths 

 resulting from superficial ostitis. The sensitive membrane lining 

 the gutter is much reduced in thickness, or represented by a yellow 

 fibrous layer with no trace of sensitive laminae. 



Causes. Frequently keratomata are preceded or accompanied by 

 complete sandcrack. Irritation of the sensitive membrane may 

 be set up by a misdirected nail, by separation of the wall, cracks 

 in the horn, by blows contracted during movement or from the hammer 

 in laying clenches or clips, which may be too tight. Horn tumours 

 may follow penetration of the white line by the clip of a displaced 

 shoe, and in a hind foot it may be caused by forging. Frohner, 

 Cadiot, and Almy admit the possibility of the occurrence of spontaneous 

 keratomata, which are sometimes met with in foals and yearlings 

 that have never worn a shoe. 



The symptoms vary with the position and size of the growth. 

 Keratomata usually, but not always, produce lameness, which 



