PATHOGENESIS 43 



fluid-containing cavity with the formation of 

 new tissue influenced by an unknown stimulus. 

 Henceforth, however, a change occurs; it 

 passes into another entirely different stage 

 through the intrusion of pyogenic microor- 

 ganisms into the cavity. 



2. Phlegmonous Stage, This is the second 

 step in the development toward a real fistulous 

 condition. Inasmuch as there is no positive in- 

 formation about the thoroughfare through 

 which infection occurs we shall only venture an 

 opinion that it is through the blood stream or 

 lymph channels that the microbes reach their 

 goal. There is, of course, the possibility that 

 cutaneous bruises from the collar may afford 

 an entrance avenue, but the fact that suppura- 

 tion occurs in animals that have never been in 

 harness and could not reasonably have sus- 

 tained contusions of sufficient severity to cause 

 subcutaneous infection, least of all, a still 

 deeper infection within the cavity without any 

 surface inflammation, leaves no doubt that at 

 least a great majority of fistulas become in- 

 fected fi^om witJiin. We have observed fistulee 

 develop rapidly from the saccular to the phleg- 

 monous stage following influenza, especially 

 complicated influenza. In fact, fistula of the 

 withers might with all reason be included as 

 one of the sequelae of influenza. The large 



