Staining Cultivation 



669 



Staining. The bacilli stain well by the ordinary methods. 

 Gram's method usually fails. 



Cultivation. The proteus is easily cultivated and grows 

 well in all the artificial media. 



Colonies. Upon gelatin plates a typical phenomenon is 

 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. Un- 

 der low magnification 

 the center of each is 

 seen to be surrounded 

 by radiations extend- 

 ing in all directions 

 into the solid gelatin, 

 and made up of chains 

 of bacilli. Between 

 the radiations and the 

 granular center bac- 

 teria are seen in active 

 motion. Upon the 

 surface the colony ex- 

 tends as a thin patch, 

 consisting of a layer of 

 bacilli arranged in 

 threads, sending nu- 

 merous projections 



from the periphery. Under certain conditions the wander- 

 ing of the processes can be directly observed under the 

 microscope. It depends not only upon the culture me- 

 dium, but, in part, upon the culture itself. Entire groups of 

 bacilli or single threads, by gradual extension and circular 

 movement, detach themselves from the colony and wander 

 about upon the plate. From the radiated central part of 

 the colony peculiar zooglea are formed, having a sausage or 

 screw shape, or wound in spirals like a corkscrew. The 

 * Flugge's "Die Mikroorganismen." 



Fig. 201. Swarming islands of proteus 

 bacilli on the surface of gelatin ; X 650 

 (Hauser). 



