68 PRACTICAL BACTERIOLOGY. 



of the nutrient medium. When this has cooled, we 

 inoculate in the usual way with the sterilised platinum 

 wire. The development of these colonies on the slide 

 varies somewhat from that of those in the test-tube ; 

 they are more even in their growth, whilst those on the 

 oblique gelatine of the test-tube develop more strongly 

 in the lower part of the tube. The greatest care must 

 be taken to remove the lid of the cultivation dish as 

 little and for as short time as possible, so as to avoid 

 the entrance of germs from the air. 



In order to prepare small plate cultivations on slides, 

 the fluid to be examined, which contains the bacteria, 

 is mixed with the liquid gelatine in the test-tube, and 

 some of this mixture is conveyed by means of a steril- 

 ised pipette to the slide. It is of the greatest import- 

 ance not to have too many germs upon the slide at 

 once ; better have only one or two than too many, for 

 in that case the effect produced by the separate colo- 

 nies is very much diminished. It is best to make 

 three attenuations of the mixture, and to prepare 

 several slides from each. When the slide cultivations 

 succeed, the colonies show up much more distinctly 

 than those on cultivation dishes. They are especially 

 useful when a microscopic examination of the edge of 

 the colony, etc., is to be made, for even with micro- 

 scopes which have only small object- stages, each 

 colony can be observed singly, and this is often im- 

 possible when cultivation dishes are used, especially 



