312 MICROBIOLOGY 



terial from which the organisms were isolated rather than the 

 method employed in the isolation. He further calls attention 

 to the fact that apparently typical B. coli gelatin colonies may 

 -be encountered which are not due to true B. coli. 



Potato. On potato the growth is rapid and abundant, 

 appearing after 24 to 36 hours in the incubator as a yellowish- 

 .brown to dark cream-colored deposit covering the greater part 

 of the surface. But there are considerable variations from the 

 typical growth on potato; there may be no visible growth at 

 -all, or it may be scanty and of a white color. These variations 

 -are due at times to the bacillus, but more often to variations in 

 the potato. 



Serum. The serum is not liquefied. On this medium 

 ^grayish, uncharacteristic colonies are developed. 



Bouillon. In bouillon Bacillus coli produces diffuse 

 -clouding with sedimentation; in some cultures a tendency to 

 pellicle formation on the surface is occasionally seen. Ford 9 

 considers the difference in the character of the growth in 

 bouillon sufficient to form varieties. In one per cent solution 

 in bouillon at 37 C. in fermentation tubes the following gas 

 production is obtained. 



In dextrose, total gas about one-half the capacity of the 



TT 2 



closed branch, ^r = - , reaction strongly acid. 



* ^^2 -*- 



In lactose, gas production, gas formula, and reaction 

 practically the same as for dextrose. 



In saccharose, total gas about two-thirds the capacity of 



TT O 



the closed bulb, ^y approximately y- . the final reaction 



;may be slightly acid or alkaline, depending upon the time 

 required for the evolution of the gas. One variety of B. coli 

 does not ferment saccharose. 



The time required for the production of the maximum 

 quantity of gas varies as a rule from one to three days in 

 <?ase of the dextrose and lactose, and from five to twenty days 

 in case of the saccharose. 



9 Ford. loc. cit. 



