108 ELEMENTS OF WATER BACTERIOLOGY. 



luted waters. Organisms of the Proteus group are some- 

 times present, exhibiting marked morphological varia- 

 tions, from the coccus form to long twisted threads and 

 forming on gelatin irregular amoeboid colonies with filiform 

 processes extending into the surrounding gelatin. The 

 B. subtilis group of strongly aerobic spore-forming bacilli, 

 giving a brown wrinkled parchment-like growth on agar, 

 and moss-like liquefying colonies on gelatin, is usually 

 represented. Among the allies of B. coli may be men- 

 tioned B. aerogenes, which differs from it in being non- 

 motile, failing to produce indol, and forming spherical 

 drop-like colonies on gelatin. B. cloacae resembles B. coli 

 in most respects, but causes a liquefaction of gelatin. 

 The property of liquefaction was formerly believed to be 

 of general significance, inasmuch as the liquefying bacteria 

 were regarded as closely allied to intestinal organisms, 

 and in themselves indicative of pollution. This position 

 is, however, no longer tenable, since many bacteria, 

 typical of the purest waters, may cause liquefaction. 



While the organisms above mentioned, and many others 

 as well, deserve notice in the examination of gelatin plates 

 from a suspected water, none of them is of sufficient 

 importance to warrant any special procedure for their 

 isolation. 



