114 FISTULA AND POLL-EVIL 



ously deform the region. Being imbedded un- 

 der firm tissues, it is often hard to the touch, 

 fluctuating only after pushing its way to the 

 surface on the side of the hgamentum nuchge 

 and pad of the mane. Evacuating the contents 

 of the sac during this stage yields an amber 

 colored fluid carrying coagulated detritus con- 

 taining no bacteria. 



This sac may sojourn indefinitely and may 

 even for a time seem to disappear entirely, only 

 to reappear subsequently. 



Evacuation and careful attention to the 

 tract and cavity may sometimes end the pro- 

 cess by slow cicatrization. Thus sometimes a 

 poll-evil is cured without a radical operation. 

 In most cases, however, the invasion of the 

 tract and cavity with extraneous microbes 

 ends in chronic fistula. 



The plilegmonous stage. In the usual course 

 of events the saccular stage ends in infection of 

 the cavity. The manner in which microorgan- 

 ism gains access to the cavity is not known, 

 but the frequency with which poll-evil is asso- 

 ciated with strangles and influenza has led us 

 to believe that these diseases play an important 

 role in its etiology ; the affected atlantoid bursa 

 serving as a focus of localization for microor- 

 ganisms contained in the blood after these dis- 

 eases. 



