72 METHODS OF CULTIVATION OF BACTERIA 



and passes through one of the two perforations with which the 

 rubber stopper of the flask is furnished. Through the other 

 opening a similar tube proceeds to the exhaust-pump. When 

 the latter is put into action the fluid is sucked through the 

 porcelain and passes over into flask b. This apparatus is very 

 good, but not suitable for small quantities of fluid. 



(6) A very good apparatus can be arranged with a lamp 

 funnel and the porcelain bougie. These may be fitted up in 

 two ways. (1) An india-rubber washer is placed round the 

 bougie c at its glazed end (vide Fig. 33). On this the narrow 

 end of the funnel d, which must, of course, be of an appropriate 

 size, rests. A broad band of sheet rubber is then wrapped 



round the lower end of the 

 i funnel, and the projecting 



...'* part of the bougie. It is 



firmly wired to the funnel 

 above and to the bougie 

 below. The extreme point 

 of the latter is left exposed, 

 and the whole apparatus, 

 being supported on a stand, 



^'% J 



FIG. 35. Muencke's modification of 

 Chamberland's filter. 



is connected by a glass tube 

 with the lateral tube of the 

 flask b ; the tube a is con- 

 nected with the exhaust- 

 pump. The fluid to be 

 filtered is placed between 

 the funnel and the bougie 

 in the space e, and is sucked 

 through into the flask b. 

 (2) This modification is shown in Fig. 34. Into the narrow part 

 of the funnel an india-rubber bung is fitted, with a perforation 

 in it sufficiently large to receive the candle, which it should grasp 

 tightly. 



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

 seen in Fig. 35. 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 cylinder b, of less diameter than the 

 cylindrical 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 



