64 BACTERIA 



The Bacillus coli communis occupies such an important 

 place in all bacteriological investigation that a few words 

 descriptive of it are necessary in this place. The " colon 

 bacillus," as it is termed, appears to be almost ubiquitous in 

 distribution. The idea once held that it belonged exclusively 

 to the alimentary canal or sewage is now discarded. It is 

 one of the most widely distributed organisms in nature, 

 though, as its name implies, its habitat is in the intestinal 

 tract of man and animals. It is an aerobic, non-sporulating, 

 non-liquefying bacillus, about .4 /* in thickness, and twice 

 that measurement in length ; hence it often appears oval or 

 egg-shaped. Its motility is in varying degree, occasionally 

 being as active as B. typhosus, but generally much less so. 

 It possesses lateral flagella. On gelatine plates at 20 C. 

 B. coli produces non-liquefying, greyish-white, round colonies; 

 in a stroke culture on the same medium, a luxuriant greyish 

 band, much broader and less restricted to the track of the 

 needle than B. typhosus. In depth of medium or " shake " 

 cultures there is an abundant formation of bubbles of gas 

 (methane or carbon dioxide) in the medium. On potato it 

 produces a light yellow, greasy growth, which must be dis- 

 tinguished from the growth of B. fluorescens liquefaciens, 

 B. pyocyaneus, and several other species on the same medium. 

 If the potato is old or alkaline, the yellow colour may not 

 appear. Milk is curdled solid in from twenty-four to forty- 

 eight hours, and a large amount of lactic acid produced. 

 In broth it produces a uniform turbidity, with later on 

 some sediment and a slight pellicle. It gives the reaction 

 to indol. 



It is now the practice to speak of the family of Bacillus coli 

 rather than the individual. The family is a very large one, 

 and shows throughout but few common characters. The 

 morphology readily changes in response to medium, tem- 

 perature, age, etc. Fermentation of sugar, coagulation of 

 milk, or indeed the indol reaction cannot always be used 



