BACTERIUM COLI COMMUNE. 307 



and are often marked at or near the middle by an oval 

 or round nucleus-like mass — the original colony from 

 which the layer on the surface developed. When located 

 in the depths of the gelatin, and examined with a low- 

 power lens, they are at first seen to be finely granular 

 and of a very pale greenish-yellow color; later they 

 become denser, darker, and much more markedly 

 granular. In shape they are round, oval, and lozenge- 

 like. When the surface colonies are viewed under a 

 low power of the microscope they present essentially 

 the same appearance as that given for the bacillus of 

 typhoid fever, viz.: they resemble flattened pellicles of 

 glass-wall, or patches of finely ground colorless glass. 

 Colonies of this organism on gelatin are frequently 

 encountered that cannot be distinguished from those 

 resulting from the growth of the bacillus of typhoid 

 fever. 



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 roots, 

 or branch-like projections from the surface growth into 

 the gelatin are sometimes seen to occur. 



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 sedi- 

 mentation. In some bouillon cultures an attempt at 

 pellicle formation on the surface may be seen, but this 

 is not always the case. In old bouillon cultures the 



