BACTERIUM COLI COMMUNE. 435 



ism on gelatin are frequently encountered that cannot 

 be distinguished from those resulting from the growth 

 of bacillus typhosus ; although, as a rule, their growth is 

 a little more luxuriant. 



In stab- and smear-cultures on gelatin the surface- 

 growth is flat, dry, and blue-white or pearl color. 

 Limited growth occurs along the track of the needle in 

 the depths of the gelatin. As the culture becomes 

 older the gelatin round about the surface-growth may 

 gradually lose its transparency and become cloudy, 

 often quite opaque. In still older cultures small root- 

 or branch-like projections from the surface-growth into 

 the gelatin are sometimes seen. At times these may be 

 of a distinctly crystalline appearance. 



It does not cause liquefaction of gelatin. 



Its growth on nutrient agar-agar and on blood-serum 

 is luxuriant, but not characteristic. 



In bouillon it causes diffuse clouding with sedimen- 

 tation. In some bouillon cultures an attempt at pel- 

 licle-formation on the surface may be seen, but this is ex- 

 ceptional. In old bouillon cultures the reaction becomes 

 alkaline and a decided faecal odor may be detected. 



Its growth on potato is rapid and voluminous, ap- 

 pearing after twenty-four to thirty-six hours in the 

 incubator as a more or less lobulated layer of a drab, 

 dark-cream, or brownish-yellow color. 



In neutral milk containing a little litmus tincture 

 the blue color is changed to red after from eighteen to 

 twenty-four hours in the incubator, and, in addition, 

 the majority of cultures cause firm coagulation of the 

 casein in about thirty-six hours, though frequently this 

 takes longer. Very rarely the litmus may indicate the 

 production of acid and no coagulation occur. 



