PCJL EVIL— CARIES OP THE JAW. 307 



or passages has become converted into a substance almost resem- 

 bling cartilage, and refuses to throw out healthy g-.-anulations, so 

 as to lead to adhesion of its walls. Here a stimulus must be 

 applied to their interior, which may be either mechanical, in the 

 shape of a seton tape passed through from end to end and left 

 there, or chemical, by means of injections. The latter are best 

 composed of chloride of zinc diluted with water. One drachm of 

 this should be mixed in a pint of water, and carefully injected 

 into every part of the sinus twice or thrice a week. 



POLL EVIL. 



Poll evil is exactly similar in its nature to fistulous withers, 

 being produced by a blow on the prominent ridge, which is situ- 

 ated on the top of the poll. The blow is* generally produced in 

 the stable, by the horse suddenly lifting his head and striking it 

 against a low beam or the lintel of the door. Or it may be caused by 

 frequently straining against the halter rein, and thus producing 

 irritation and inflammation of the part. As the ligamentum colli 

 is attached above, and anterioi to, the inflamed part, when matter 

 forms it is confined and gives intense pain; besides which, it is a long 

 time before it opens a passage by natural means. The symptoms 

 are a painful swelling on the poll, of a soft nature, accompanied by 

 the sense of fluctuation on examination, just like that described as 

 accompanying fistulous withers. The treatment must be precisely 

 similar to that described in the last section ; but as the matter 

 when formed lies very close to the spinal cord, some caution must 

 be exercised in adopting stimulating injections, which are apt to 

 produce severe inflammation, likely to extend to these important 

 structures. So also in opening it, the knife should not be carried 

 deeply into the situation of the spinal marrow, which here iie.= 

 exposed, and is easily divided (as in the operation known by the 

 name of pithing), but it should be used in a slanting manner, again 

 selecting the right side in preference to the left. A seton is here 

 the safest plan for promoting granulation and adhesion, and as the 

 fistulous track is seldom very long, the tape will work its wav 

 gradually out, by which time the cure is efi'ected. 



CARIES OF THE JAW. 

 The DPPiSR JAW, from its exposed situation, and the 

 lower from the same cause, and also from the ^abuse of the bit, 

 are liable to mechanical injury, which ends in caries (ulceration), 

 or sometimes in necrosis (mortification) of the part. Caries of 

 thejf lower jaw, between the tushes and grinders, is extremely 

 common, owing to the barbarous punishment which is inflicted by 

 the use of long levers to curb bits, together with light curb chains. 

 The bony plate forming the roof of the mouth is also often iniured 



