27-1 BACTERIOLOGICAL EXAMINATION OF WATER. 



so as to avoid contaminating the broth. Bv opening the 

 pinch-cock 10 c.c. of the broth from the mantle were now 

 allowed to filter through the bougie into the flask. The filtra- 

 tion occurred simply as the result of atmospheric pressure, and 

 the bougie worked under conditions which would allow its 

 molecular influence full play. The apparatus was then placed 

 in an incubator, the temperature of which averaged 25 C. 

 After twenty-four hours exposure to this temperature the broth 

 in the mantle and flask was found perfectly clear, showing that 

 the manipulations had been performed without introducing any 

 contamination. The broth in the mantle was then inoculated 

 with a loopful of a twenty-four hours agar culture of B. typho- 

 sus. Next day the broth in the mantle was found uniformly 

 turbid, but the broth in the flask was perfectly clear; the 

 pinch-cock was then opened and 10 c.c. allowed to filter through 

 into the flask. On the following day the broth in the flask 

 being still perfectly sterile, 10 c.c. were again filtered through 

 from the mantle. The same filtration process was continued 

 day by day, and the amount of broth filtered each day from the 

 mantle was replaced by fresh sterile broth, the manipulation 

 being carried out with every precaution. The broth in the 

 flask remained perfectly clear for four days, showing that there 

 was no imperfection in the connections of the filtering bougie 

 with the Kitasato flask. On the fifth day of filtration, however, 

 the broth in the flask was found slightly turbid. A ioopfu] 

 was then withdrawn from the contents of the flask by means of 



