BACTERIA IN WATER 



43 



centrated emulsion of the bacteria of the original water, 

 phenol-gelatine plates or Eisner plates (both acid media) 

 may be readily made. In this way we not only catch many 

 bacteria which would evade us if we were content with the 

 examination merely of a few drops of the water, but we 

 eliminate by means of the acid those common water bacteria, 



O 



c 



like Bacillus fluorescens liquefaciens, which so greatly confuse 

 the issue. 



In the course of two or three days the film of gelatine 

 on the plate becomes covered with colonies of germs, and the 

 next step is to examine these quantitatively and qualitat- 

 ively. We may here insert a simple scheme by which this 

 may be most fully and easily accomplished : 



I. Naked-Eye Observation of the Colonies. By this means 



