MICROORGANISMS IN WATER. 193 



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) natural 

 water bacteria; (b) soil bacteria from surface washings; (c) intestinal 

 bacteria, usually of sewage origin. But there is no strict dividing 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 generally 

 regarded as harmless to man. These organisms are frequently numerous 

 in river, lake, and all surface waters; certain species predominate 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 pro- 

 duces in gelatin. 



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

 not liquefy gelatin, but produces characteristic colonies with a fluorescent 

 shimmer, is often very abundant in river waters, and is representative of 

 a group comprising B.f. longus, B.f. tennis, B.f. aureus, and./. 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. 



Chromogenic bacilli and cocci (Groups XIII, and XI V) 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. indicus, 

 B. rubescens, and B. rubefaciens. Several yellow and orange organisms 

 are commonly found, such as B. aquatilis, B. ochraceus, B. aurantiacus, 

 B.fulvus, etc. 



At certain times, particularly in river and brook waters, organisms 



