44 BACTERIA IN WATER 



low degree, and this, of course, is the reason for quantitative 

 estimations. 



Quality of Water Bacteria 



The species of bacteria found in water vary widely. Many of 

 them are common in pure water, and may be strictly termed 

 " water bacteria " ; others are as clearly " sewage bacteria," with 

 an allied group belonging to the soil and washed into rivers, or 

 wells, by rain, and which may be described as "surface bacteria"; 

 and a third group are the pathogenic bacteria, which have under 

 exceptional conditions been isolated from water. Prof. Marshall 

 Ward, in his fifth report to the Water Kesearch Committee of the 

 Koyal Society, drew up a classification of water bacteria,* which was 

 adopted two years later by Boyce and HilLf In 1899 Johnson 

 and Fuller made other groups,! and many other workers have sug- 

 gested classifications. The two most recent have been constructed 

 by Horrocks of Net ley and Jordan of Chicago. (| 



Both authorities recognise that provisional classification is all that 

 is at present possible. Their groups are as follows : 



CLASSIFICATION OF HORROCKS. 



GROUP 



i. Fluorescent bacilli. 



ii. B. aquatilis sulcatus. 



iii. B. subtilis and " Potato bacilli." 



iv. B. liquefaciens. 



v. Chromogenic (red) bacilli. 



vi. Chromogenic (yellow) bacilli. 



vii. Chromogenic (blue) bacilli, 



viii. Chromogenic (milk-white) bacilli. 



ix. Chromogenic (brown) bacilli. 



x. Micrococci. 



xi. Sarcinae. 



xii. Spirilla. 



xiii. Denitrifying and nitrifying bac- 

 teria. 



xiv. B. coll communis. 



xv. B. enteritidis sporogenes. 



xvi. Staphylococci. 



xvii. Streptococci, 



xviii. The Proteus group. 



xix. Sewage bacteria. 



xx. B. typhosus. 



CLASSIFICATION OF JORDAN. 

 GROUP 



i. B. coli communis. 

 ii. B. lactis aerogenes. 

 iii. Proteus, 

 iv. B. enteritidis. 

 v. B. fl,uorescens liquefaciens. 

 vi. B. fluorescens non-liquefacients. 

 vii. B. subtilis. 



viii. Non-gas forming, non-fluorescent, 

 non-sporulating, liquefy gela- 

 tine and acidify milk, 

 ix. Similar to Group viii., but milk 



rendered alkaline. 

 x. Similar to Group viii. , but gelatine 



not liquefied. 

 xi. Similar to Group ix. , but gelatine 



not liquefied, 

 xii. Similar to Group xi., but the 



reaction of milk not altered, 

 xiii. Chromogenic bacilli, not included 



in above groups. 



xiv. Chromogenic Staphylococci. 

 xv. Non-chromogenic Staphylococci. 

 xvi. Sarcinse. 

 xvii. Streptococci. 



* Proc. Roy. Soc., 1897, Ixi., p. 415. 



t Jour, of Path, and Bact., 1899, vi., p. 32. 



J Jour, of Exp. Med., 1899, iv., p. 609. 



An Introduction to the Bacteriological Examination of Water, 1901, p. 42 et sey. 



II Jour, of Hygiene, 1903, vol. iii., tfo. 1, p. 5. 



