FILTRATION OF CULTURES. 



77 



FlG. 42. Muencke's modification 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, A 



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 



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 in the porcelain cylinder, and the 

 whole top covered, as shown at /, 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 

 FiG. 43 . Flask a f ter being dried is to be passed carefully through 



fitted with porce- & _ 



lain bougie for fii- a Bunsen flame, to burn off all organic matter. It 

 tering large quan- the j tter is a ii owec } 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, 



