58 MANUAL OF BACTERIOLOGY. 



the bacteria (Fig. 16). These fluids usually filter very slowly, 

 and filtration has to be assisted by some form of vacuum- 

 pump; usually the filter-pump, which is used in connection 

 with a stream of running water, is employed. Compressed air 

 or carbonic acid may be used to assist in forcing fluids through 

 the filter. The filter bougies, the flasks and all parts of the 

 apparatus must, of course, be steriHzed by heat before and after 

 using. 



