118 FISTULA AND POLL-EVIL 



tacked from without. Its dorsal face is at- 

 tack first, while in the other, the under part 

 at the atlantal bursa, is attacked before the 

 upper part becomes involved. 



This form of fistula can only be recognized 

 as such at the early stage, for once spread 

 deeply into the poll it has no differentiating 

 qualities. 



Etiology 



The cause of poll-evil, like that of fistula of 

 the withers, is by no means settled. The aca- 

 demic explanation (traumatism) that seems to 

 have satisfied all past writers on the subject 

 entirely lacks confirmation. Wherever this 

 subject is discussed verbally or in literature the 

 matter of etiology is always indifferently 

 passed over as if it is a settled fact that poll- 

 evil is a traumatism. No one seems to have 

 ever questioned seriously the theory of trau- 

 matic origin in spite of the fact that no one 

 seems to have ever actually traced a typical 

 poll-evil to any definite traumatism. The 

 truth seems to be that traumatism plays no 

 part whatever in its cause. Except in the rare 

 case that originates with a wound of the poll 

 it is plain that we must seek farther for a rea- 

 sonable theory of cause. It is our opinion that 

 the cause is unknown, that the serous sac that 

 starts it develops under influences we cannot 



