194 MICROBIOLOGY OF WATER AND SEWAGE. 



producing violet pigment are quite common. B. violaceus or B. janthi- 

 nus, as it is sometimes called, is the prevailing type; others are B. lividus, 

 B. amethystinus, and B. coeruleus. 



The chromogenic cocci produce either orange or yellow pigment, and 

 as a rule are not numerous in water. Sarcina lutea is the most common 

 species. 



Non-chromogenic cocci (Group XV) are more frequent. M. candi- 

 cans, M. nivalis, M. aquatilis, are non-liquefying forms, and M. coronatus 

 is the type of those which liquefy gelatin. 



SOIL BACTERIA FROM SURFACE WASHINGS. During times of flood, 

 high water, and after rains, numerous soil organisms are found in natural 

 waters; and occasionally certain species persist for a considerable time. 

 Among the commonest species is B. mycoides, with its characteristic 

 rhizoid colony; also B. subtilis, B. megatherium, and B. mesentericus vul- 

 gatus, with its allied varieties; likewise B. m. fuscus and B. m. ruber all 

 belonging to Jordan's Group VII, and having many characters in common, 

 such as characteristic colonies, followed by liquefaction when growing in 

 gelatin, production of spores, etc. 



Cladothrix dichotoma, one of the thread bacteria, easily recognized on 

 gelatin plates by the brown halo that surrounds the colony, is often found 

 in fresh and stagnant water, and in most soils. It seems to flourish where- 

 ever there is much organic matter. 



These are the soil organisms most often found when beef peptone gel- 

 atin is used for isolating purposes; but if other media are used, a different 

 flora appears, and we find nitrifying organisms, yellow chromogens, etc. 



INTESTINAL BACTERIA, USUALLY OF SEWAGE ORIGIN. Proteus Group. 

 There are several groups of sewage organisms found in impure water; 

 some of these are very abundant in crude sewage, but are not found 

 in such relatively large numbers in contaminated water. Jordan's 

 Group III contains the organisms belonging to the large proteus group, 

 the principal species being B. vulgaris, B. zenkeri, B. mirabilis, B. zopfii, 

 the sewage proteus of Houston, and B. cloaca. All these are frequently 

 found in impure water, and in sewage. In the latter Houston has found 

 as many as 100,000 per c.c. All these organisms are motile, liquefy 

 gelatin, and produce gas in dextrose and saccharose broth, and little or none 

 in lactose; reduce nitrates, curdle milk, produce indol, and give a fecal, 

 disagreeable odor in broth or other media. 



Sewage Streptococci. The streptococci found in sewage are probably 



