INTRODUCTION 9 



bursa of the ligamentum nuchge and by some 

 writers as inflammation of the ligament itself. 

 No one has thus far been able to prove its def- 

 inite cause. Like fistula of the withers, ap- 

 parently for want of an explanation based on 

 demonstrable facts, it has always been attrib- 

 uted to bruisings of the poll. 



While we do not entirely eliminate traimia- 

 tism as the cause of some cases of poll-evil and 

 some attacks of fistula of the withers, it has 

 been our experience that when injuries are the 

 cause, the wound or bruise is always apparent 

 and the disease advances into the depths of the 

 region by gradual stages from the initial focus 

 deeper and deeper until the interior is finally 

 attacked by the encroaching pyogenic process. 

 In ordinary cases of both of these afflictions, 

 the initial focus is always central, far down in 

 the depths of the body where external violence 

 can have but little influence. From this cen- 

 tral location the disease as gradually advances 

 in the outward direction in the ordinary case, 

 as it does inward in the exceptional cases due 

 to trauma. We have, therefore, no choice 

 than that of describing both poll-evi] and fis- 

 tula of the withers as having two distinct caus- 

 es, one a wound or bruise at the very surface, 

 and the other, and commonest, as yet imknown. 



The prevalence of fistula of the withers and 



