MICROORGANISMS IN WATER 311 



the soil bacteria, are found only at certain seasons, as after rain or dur- 

 ing flood- time, and flourish only for a time; while some few, such as 

 intestinal organisms that find their way into water, survive for only 

 a short period. 



CLASSES OF BACTERIA FOUND IN WATER 



The bacteria found in water are here roughly divided into: (a) natu- 

 ral water bacteria; (b) soil bacteria from surface washings; (c) intes- 

 tinal bacteria, usually of sewage origin. But there is no strict divid- 

 ing line between these three groups; for some organisms belonging to 

 the water flora are found in the soil, and vice versa. Water draining 

 from manured land frequently contains intestinal organisms. The 

 division, however, is sufficient for all practical purposes. 



NATURAL WATER BACTERIA. The natural water bacteria are gen- 

 erally regarded as harmless to man. These organisms are frequently 

 numerous in river, lake, and all surface waters; certain species predomi- 

 nate at one season, and disappear at another. Some of the best known 

 are mentioned below. Several investigators have grouped the bacteria 

 found in water into classes according to their biochemical properties. 

 Where groups are subsequently referred to, the classification is that 

 used by Jordan and followed by many other workers. 



B. fluorescens liquefaciens, Group V, together with some closely allied 

 varieties, is probably more frequently found in water than any other 

 form, and is easily recognized by the green fluorescence and liquefaction 

 it produces in gelatin. 



B. fluorescens non-liquefaciens, Group VI, as the name implies, does 

 not liquefy gelatin, but produces characteristic colonies with a fluores- 

 cent shimmer, is often very abundant in river waters, and is representa- 

 tive of a group comprising B. f. longus, B. f. tennis. B. f. aureus, and 

 B. f. crassus. 



Certain organisms which liquefy gelatin and acidify milk classed by 

 Jordan in his Group VIII are quite common at certain seasons. 

 Some of these are soil organisms and are closely related to the proteus 

 group; and some of them are B. liquefaciens, B. punctatus, B. circulans. 



Chromo genie bacilli and cocci (Groups XIII, and XIV) are often 

 present in water. Of those producing red coloring matter, the well- 

 known B. prodigiosus is the type of the group; others are B. ruber, B. 



