370 



Suppuration 



observed in connection with the development of the colonies, 

 for the most advantageous observation of which the medium 

 used for making the cultures should contain 5 instead of 10 

 per cent, of gelatin. Kruse * describes the phenomenon as 

 follows: "At the temperature of the room, rounded, saucer- 

 shaped depressions, with a whitish central mass surrounded 

 by a lighter zone, are quickly formed. Under low magni- 

 fication the center of each is seen to be surrounded by 

 radiations extending in all directions into the solid gelatin, 

 and made up of chains of bacilli. Between the radiations 



Fig. 112. Swarming islands of proteus bacilli on the surface of gelatin; 

 X 650 (Hauser). 



and the granular center bacteria are seen in active motion. 

 Upon the surface the colony extends as a thin patch, con- 

 sisting of a layer of bacilli arranged in threads, sending 

 numerous projections from the periphery. Under certain 

 conditions the wandering of the processes can be directly 

 observed under the microscope. It depends not only upon 

 the culture-medium, but, in part, upon the culture itself. 

 Entire groups of bacilli or single threads, by gradual exten- 

 sion and circular movement, detach themselves from the 

 colony and wander about upon the plate. From the radi- 



* Flugge's " Die Mikroorganismen." 



