398 PATHOGENIC MICROORGANISMS 



upon a temporary depression of one or another cultural characteristic of 

 Bacillus coli communis, while others can be definitely included within 

 other closely related, but distinct groups. 



That secondary features, such as dimensions, motility, and luxuri- 

 ance of growth upon various media, may be markedly altered by arti- 

 ficial cultivation is a common observation. It has nof* however, been 

 satisfactorily shown that cardinal characteristics, such as the forma- 

 tion of indol from pepton, or the power to produce gas from dextrose 

 and lactose, can be permanently suppressed without actual injury or 

 inhibition of the normal vitality of the microorganism. Such alter- 

 ation is, in fact, contrary to experience, which demonstrates that 

 whenever such changes do occur, they are purely temporary and a few 

 ^operations of cultivation under favorable environmental conditions 

 will regularly restore the organism to its normal activity. 



Bacillus coli communior. Distinct and constant varieties of Bacil- 

 lus coli, however, do occur. The most common of these is one whicb 

 Dunham has named Bacillus coli communior, because of the fact that 

 he believes it to be more abundant in the human and animal intestine 

 than is coli communis itself. This bacillus possesses all the cardinal 

 characteristics of the colon group. It is a Gram-negative bacillus, 

 moderately motile, non-sporulating, and morphologically indistinguish- 

 able from the communis variety. It does not liquefy gelatin, it 

 produces indol from pepton, coagulates and acidifies milk, and grows 

 characteristically upon agar and potato. It differs from Bacillus coli 

 communis in that it produces acid and gas from saccharose as well as 

 from dextrose and hictose, whereas the former does not form acid 'or 

 gas from "saccharose. 



