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 ligamentum nuche 
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 phlegmonous stage. Inthe 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 microér- 
ganisms contained in the blood after these dis- 
eases. 
