326 Suppuration 



"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 magnification the center of each is seen to be surrounded by radiations ex- 

 tending in all directions into the solid gelatin, and made up of chains of bacilli. 

 Between the radiations and the granular center bacteria are seen in active motion. 

 Upon the surface the colony extends as a thin patch, consisting 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 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 younger colonies, which have not yet reached the surface 

 of the gelatin, are more compact, rounded or nodular, later covered with hair-like 

 projections, and becoming radiated like the superficial colonies." 



Fig. 116. Swarming islands of proteus bacilli on the surface of gelatin; X 650 



(Hauser). 



If the culture-medium be concentrated, or the culture have been 

 frequently transplanted, the phenomenon is less marked or may 

 not occur. 



Bouillon. In this medium the organism grows rapidly, and 

 quickly clouds the fluid. A pellicle soon forms upon the surface and 

 a mucilaginous sediment occurs later. 



Gelatin Punctures. Puncture cultures in gelatin are not char- 

 acteristic. A stocking-like liquefaction occurs in the gelatin and 

 extends so rapidly that the entire medium is liquefied in a few days. 

 Anaerobic cultures do not liquefy. 



Agar-agar. Upon agar-agar the bacillus forms a moist, thin, 

 transparent, rapidly extending layer which rarely reaches the sides 

 of the tube. Upon agar-agar plates ameboid movement of the 

 colonies sometimes occurs. 



