THE FILTRATION OF CULTURES 



73 



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. 36 may be used. The tap in 

 its bottom enables the filtrate to be 

 removed without the apparatus 

 being unshipped, but it is difficult 

 to get the tap to fit so accurately as not to 

 allow air to pass into the vacuum chamber. 

 For filtering small quantities of fluid the 

 apparatus shown in Fig. 37 may be used. 

 It consists of a small Chamberland bougie 

 fitted by a rubber tube to a funnel, the stem 

 of which has been passed 

 through a rubber cork ; 

 this cork fits into a tri- 

 angular flask with side 

 arm for connection with 

 exhaust. 



Before any one of 

 the above apparatus is 

 used, it ought to be con- 

 nected up as far as pos- 

 sible and sterilised in 

 the Koch's steriliser. 

 The ends of any im- 

 portant unconnected 

 parts ought to have pieces of cotton wool 

 tied over them. After use the bougie is 

 to be sterilised in the autoclave, and after 

 being dried is to be passed carefully through 

 a Bunsen flame, to burn oft 7 all organic 

 matter. If the latter is allowed to accumu- 

 late the pores become filled up. 



The success of filtration must be tested 

 by inoculating tubes of media from the 

 filtrate, and observing if growth takes place, 

 as there may be minute perforations in the 

 candies sufficiently large to allow bacteria 

 to pass through. Filtered fluids keep for a long time if the 

 openings of the glass vessels in which they are placed are kept 



FIG. 36. Flask fitted 

 with porcelain 

 bougie for filtering- 

 large quantities of 

 fluid. 



FIG. 37. Flask for 

 filtering small quanti- 

 ties of fluid. 



