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 Waber Eesearch Committee of the 

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

 adopted two years later by Boyce and Hill.f 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.il 



Both authorities recognise that provisional classification is all that 

 is at present possible. Their groups are as follows : — 



CLASSIFICATION OF HOREOOKS. 



GROUP 



i. 



ii. 

 iii. 

 iv. 



V. 



vi. 

 vii. 

 viii. 



ix. 



X. 



xi. 

 xii. 

 xiii. 



xiv. 



XV. 



xvl. 



xvii. 



xviii. 



xix. 



XX. 



Fluorescent bacilli. 

 B. aquatilis sulcatus. 

 B. suhtilis and " Potato bacilli." 

 B. liquefadens. 

 Chromogenic (red) bacilli. 

 Chromogenic (yellow)' bacilli. 

 Chromogenic (blue) bacilli. 

 Chromogenic (milk-white) bacilli. 

 Chromogenic (brown) bacilli. 

 Micrococci. 

 Sarcinse. 

 Spirilla. 



Denitrifying and nitrifying bac- 

 teria. 

 B. coli communis. 

 B. enteritidis sporogenes. 

 Staphylococci. 

 Streptococci. 

 The Proteus group. 

 Sewage bacteria. 

 B. 



OLASSIPICATION OF JORDAN. 



GROUP 



i. B. coli communis. 

 ii. B. lactis aSrogenes. 

 iii. Proteus, 

 iv. B. enteritidis. 

 V. B. Jluorescens liquefadens. 

 vi. B. jluorescens non-liquefaciens. 

 vii. B. suhtilis. 



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-chromogenlc Staphylococci, 

 xvi. Sarcinse. 

 xvii. Streptococci. 



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



t Joiir. of Path, and Bad. , 1899, vi., p. 32. 



t Jour, of Mxp. Med., 1899, iv., p. 609. 



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



II Jour, of Hygiene, 1903, vol. iii.. No. 1, p. 5. 



