xvi] VIBRIO AND SPIRILLUM 421 



and then with a droplet of this inoculate nutrient gelatine, 

 contained in a test-tube, liquefy this in warm water, shake 

 up and then pour it into sterile glass dishes for the object 

 of plate cultivation. A particle of a mucus flake of a rice- 

 water stool rich in the comma bacilli first diluted in several 

 cubic centimetres of sterile salt solution and a trace of this 

 mixture being used for plate cultivation yields large numbers 

 of colonies of the comma bacilli. These show themselves (at 

 20° C.) already after thirty to forty hours as greyish-white 

 minute specks just visible to the unaided eye ; after two to 



Fig. 172. — Plate Cultivations in Nutritive Gelatine, after three Days 

 Growth at 2o''C., seen with the unaided Eye. 



Colonies of cholera comma-bacilli. 

 The clear part is due to liquefaction of the gelatine. 



three days they are distinctly visible as clear, circular de- 

 pressions, due to liquefaction of the gelatine within this 

 depression. In the centre of the depression is a round, 

 greyish mass surrounded by clear, liquefied gelatine ; looked 

 at under a magnifying glass this mass appears like a mass of 

 minute glass splinters, with a more or less uneven margin ; 

 in the centre of the mass is a more opaque larger granule. 

 Each of the colonies gradually enlarges ; the zone of clear, 

 liquefied gelatine becomes broader, and the whitish central 

 granular patch enlarges ; where the colonies lie closely to- 

 gether at the outset, the progressing liquefaction produces 



