FILTRATION OF CULTURES. 



17 



FjG. 42. — Muencke's modiftcalion of 

 Chamberland's filter. 



(c) Muencke's modification of the Chamberland principle is 

 seen in Fig. 42. It consists of a thick-walled flask, a, the lower 

 part conical, the upper cylindrical, with, a strong flange on the 

 lip. There are two lateral tubes, ^ 



one horizontal to connect with 

 exhaust-pipe, and one sloping, 

 by which the contents may be 

 poured out. Passing into the 

 upper cylindrical part of the 

 flask is a hollow porcelain cylin- 

 der b, of less diameter than the 

 cyhndrical part of flask a. It is 

 closed below, open above, and 

 rests by a projecting rim on the 

 flange of the flask, an asbestos 

 washer, c, being interposed. The 

 fluid to be filtered is placed in the porcelain cylinder, and the 

 whole top covered, as shown at f, with an india- 

 rubber cap with a central perforation ; the tube d 

 is connected with the exhaust-pump and the tube e 

 plugged with a rubber stopper. When 

 a large quantity of fluid is to be filtered, 

 a receptacle such as that shown in Fig. 43 may be 

 used. The tap in its bottom enables the filtrate 

 to be removed without the apparatus being un- 

 shipped, but it is difficult to get the tap to fit so 

 accurately as not to allow air to pass into the 

 vacuum chamber. 



Before any one of the above apparatus is used, 



it ought to be connected up as far as possible and 



sterilised in the Koch's steriliser. The ends of 



any important unconnected parts ought to have 



pieces of cotton wool tied over them. After use 



the bougie is to be sterilised in the autoclave, and 



F1G.43.— Flask after being dried is to be passed carefully through 



lain bougie for fii- a Bunscu flame, to burn off all organic matter. If 



tenng large quan- ^^ latter is allowed to accumulate, the pores become 



titles of fluid. ' ^ 



filled up. 

 The success of filtration must be tested by inoculating tubes 

 of media from the filtrate, and observing if growth takes place, 



