60 BACILLUS TYPHOSUS 



If such a colony is examined with a high power it 

 is seen to be composed of numerous short, thick, 

 round-ended bacilli (about 2 p by "8 /i), which are 

 present either as single cells or occasionally as short 

 chains. They are generally heaped together so that 

 individual bacilli can hardly be distinguished except 

 at the margins (Fig. 51). 



The bacilli in sections stain with methylene-blue 

 and fuchsine, but are easily decolorised, and are 

 therefore not easily differentiated. This, organism 

 does not stain by the method of Gram. 



From such infected organs, especially the spleen 

 and gall bladder, pure cultures may be obtained by 

 employing any of the usual separation methods. 

 Should gelatine plate cultures kept at 21° C. be 

 employed, colonies develop which, at first small, 

 rather clear, and very faintly granular, gradually, if 

 on the surface, assume the characters seen in Fig. 52. 

 The colony is greyish white, somewhat transparent, 

 and iridescent. It is raised in the centre and presents 

 a thin, spreading, festooned margin. The surface is 

 marked by groovings and ridges which run from the 

 centre to the periphery, but are crossed by other 

 ridges concentrically arranged. The figure shows 

 well the superficial markings, but exaggerates the 

 sharpness. of outline and the raised character of the 



