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 fistulae become in- 
fected from within. We have observed fistulz 
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 sequele of influenza. The large 
