QUALITY OF WATER BACTERIA 45 



Both the above quoted authorities furnish a large body of facts 

 illustrative of the characteristics of the various groups suggested, to 

 which the reader is referred for further particulars. Broadly it may 

 be said that the organisms classified in twenty groups by Horrocks 

 are divisible into a few general divisions. Groups i.-xii. are the 

 ordinary water bacteria ; Group xiii. is the denitrifying and nitrify- 

 ing organisms found in soil, water, etc. ; Groups xiv.-xix. are the 

 sewage bacteria ; and Group xx. represents the pathogenic group of 

 organisms occurring occasionally in water. Brief reference will 

 now be made to these four groups, with the exception of the second, 

 which will be dealt with subsequently. 



(a) Ordinary Water Bacteria. — These are organisms usually 

 found in pure or approximately pure waters. They are common in 

 well waters and unpolluted river water. They include the common 

 fluorescent bacilli, liquefying and non-liquefying, and which create 

 an iridescent green colour in the nutrient media. In this class also 

 are B. aguatilis sulcatus, the "potato bacilli" {B. mesentericus, 

 mdgatvs, fuscvs, et ruber), the " hay bacilli " (B. subtilis, B. mycoides, 

 B. megatheriu7n), the liquefying bacilli common in unfiltered waters, 

 the chromogenic organisms (B. prodigiosus, B. lactis erythrogenes, 

 B. rubescens, B. arhorescens, B. aquatilis, B. aurantiacus, B. violaceus, 

 etc.), and the micrococci, sarcinae, and ordinary water spirilla.* The 

 presence of these species of bacteria in water, unless in very 

 exceptional numbers, indicates little of importance. They vary 

 according to season, geological formation over or through which the 

 water passes, surface washings, aeration of the water, forms of 

 vegetation existing in the water, and many other similar natural 

 conditions. The fluorescent and non-gas-producing and non-liquefy- 

 ing bacilli are generally less abundant in recently polluted waters 

 than in purer waters, and non-chromogenic staphylococci more 

 abundant. 



(b) Sewage Bacteria. — This group includes B. coli communis and 

 its allies, the Proteus family, B. enteritidis sporogenes of Klein, and 

 certain streptococci and staphylococci. They will be treated of 

 subsequently in a chapter devoted to the bacteriology of sewage (see 

 pp. 152-157). Exception will, however, be made in the case of B. coli 

 communis, as this organism is perhaps the most important in relation 

 to water. It will, therefore, be considered here. In the first place 

 the chief biological and cultural facts may be stated, and in the 

 second place a general note may be added. 



* The biological characters of these various groups of water bacteria will be 

 found in Frankland's Micro-organisms in Water, pp. 399-,508 ; Lehmann and 

 Neumann's Bacteriology, vol. ii., pp. 133-381; Crookshank's Bacteriology and 

 Infective Diseases ; Horrocks' Bacteriological Examination of Water, pp. 42-80 ; and 

 in the systematic works of Sternberg, Flflgge, Besson, Mace, etc. 



