BACILLUS PROTEUS VULGARIS. 595 



like the colon bacteria in shape, others are found as very 

 long filaments, and occasionally sporulina-forms are met 

 with. True spirilla-forms are never found. All the 

 forms mentioned may be met with in cultures of the 

 same organism. The diameter of the bacillus is usually 

 about 0.6 /i, but the length varies from 1.2 ft or less to 4 // 

 or more. No spores are formed. The organisms are 

 actively motile. The long filaments frequently form loops 

 and tangles. Flagella are present usually in large num- 

 ber; upon one of the longer bacilli as many as one hun- 

 dred have been counted. Involution-forms are frequent 

 in old cultures. The bacilli stain well by the ordinary 

 methods. Gram's method is irregular in action, but 

 usually fails to color the bacteria. 



Upon gelatin plates a typical phenomenon is observed 

 in connection with the development of the colonies, but 

 for the most advantageous observation the gelatin used 

 for making the cultures should contain only 5 per cent, 

 of gelatin instead 10 per cent, as ordinarily used. Kruse 1 

 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 magnification the center of 

 the growth 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 motile 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. Occa- 

 sionally filaments are found in the surroundings. 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, 

 bv gradual extension and circular movement, detach 

 themselves from the colony and wander about upon the 



1 Fliigge's Mikroorganismtn. 



