56 FISTULA AND POLL-EVIL 
a well defined limiting wall is likewise not un- 
derstood. It simulates tumor formation, 
3. Typical fistule develop deep secondary 
abscess during the early phase of the phleg- 
monous stage, while atypical ones develop these 
only in the later stages. The early abscess 
cavities of the latter are superficial. 
4. Fibrosis, that is, the formation of fibrous 
tissue is more pronounced in the typical form 
and is never voluminous in the other. 
5. Bone involvement is more certain and al- 
ways more extensive in the atypical forms. 
6. The toxemia is more pronounced in the 
early stages of the typical form, but in later 
stages both are alike in this connection. 
