igo 



MICRO-ORGANISMS AND DISEASE [chap. 



motility may be observed on many individuals. The same 

 holds good for artificial cultures — plates, surface gelatine 

 and surface Agar, broth and milk cultures — for here also in 

 young cultures, as a rule, only a minority show motility, in 

 old cultures the motile individuals are rare. 



Bacillus coli forms typical colonies on the surface of gela- 

 tine at 20° C. ; after twenty-four hours they are recognisable 



Fig. 61. — A Stab Culture and a Shake Culture in Gelatine of Bacillus 

 CoLi, with Gas Bubbles. 



as flat, translucent, greyish, roundish, but angular patches, 

 slightly thickened in the middle part or near one margin ; 

 after forty-eight hours the patches are considerably enlarged, 

 angular, thin and filmy, and translucent in the marginal, 

 thick and less translucent in the middle part. The whole 

 patch is dry, whitish in reflected light, and under a magni- 

 fying glass appears fairly homogeneous, though after several 



