CULTURAL CHARACTERS 



643 



Fig. 13-i. — Proteus vulgaris, 



showing swarming on agar, 6 

 hours, 37° C. (X 8). 



cyclone. There is some \ ariation in depth of staining. Except for non-flagellated 

 variants, all members are actively motile by peritrichate flagella in young cultures. 

 Neither spores nor capsules are formed. The 

 reaction to Gram's stain is uniformly negative. 



Cultural Characters. — Growth occurs freely on 

 the usual media. One of the most characteristic 

 properties of Proteus strains is their ability to 

 " swarm " on solid media. Cantu (1911), who 

 made a study of this feature, found that if an 

 organism of the Proteus group was inoculated into 

 the water of condensation of an agar slope, a 

 rapid growth occurred, which spread over the 

 whole surface, producing a uniform layer hardly 

 distinguishable from the medium. This process 

 has been more fully described by Moltke (1927, 

 1929). " Swarming " may be defined as a " pro- 

 gressive surface spreading by the microbes from 

 the edge of the parent colony." It is best studied 

 by touching the centre of an agar plate with a 

 needle dipped in a Proteus culture. First of all 

 a colony develops, and then after about 6 hours 



at 37° C. a thin, effuse, ground-glass type of growth appears round the edge 

 of the colony, and rapidly spreads over the whole plate (Fig. 134). If it is 

 examined under the microscope, it is seen that, when swarming commences, long 



slender rods in continuous motion 

 X break away from the periphery of 



the colony, and, after travelling 

 some distance from th^ parent 

 colony, join neighbouring lateral 

 offshoots, to form arches, which 

 are rapidly filled with other rods 

 i from within. Whole rafts of rods 

 tear loose from the peninsula so 

 formed, and work across the agar, 

 so that in a short time the colony 

 / \ "^ " '"^""^ ^^ is surrounded by an archipelago of 



islands and solitary organisms, all 

 ^ ^ "~ constantly in motion. The very 



long rod forms are the predominant 

 feature in the picture ; they form 

 arches, islands, spirals, and ques- 

 tion-mark forms (Fig. 135). Once 

 the plate is completely covered 

 with " swarmers ", the long rods 

 are replaced by quite short forms 

 (Figs. 136 and 137). The property of swarming is observed only on the sur- 

 face of solid media. In the depths of an agar shake or pour plate culture the 

 colonies are compact. This circumstance may be made use of in the isolation of 

 organisms mixed with Proteus bacilli (Fry 1932). Other methods for the inhibition 



/ 



\^ 



Fig. 135. — Proteus vulgaris. 



From an agar culture, 6 hours, 37° C, showing 

 long filaments ( X 1000). 



