4S BACTERIOLOGICAL EXAMINATION OF WATER. 



nail-head appearance. The bacillus is not motile. It is said to be 

 identical with the B. iris of Frick, and to be often found in air 

 and water. 



I have frequently isolated this organism from water. The 

 nail- headed colonies when fished and planted out in gelatine 

 produce a marked green fluorescence of the medium ; the growth 

 on the surface sometimes remains thick, at other times it pro- 

 duces a thin layer like the stab of B. fluorescens non-liquefaciens. 

 The organism noes not coagulate milk, produce indol, nor form 

 gas in glucose-gelatine. The growth on potato is greenish- 

 yellow. It does not reduce nitrates appreciably. In nearly all 

 its cultural reactions it resembles B. fluorescens non-liquefaciens, 

 and according to Fliigge it is only a variety of this organism. 



The bacilli above described form the most important varieties 

 of the B. fluorescens non-liquefaciens which are found in pure 

 water. They are important because in the early days of bac- 

 teriological study they were sometimes mistaken for the B. 

 typhosus. When the green fluorescence is not present, which 

 happens if the organism is enfeebled, the colonies have a super- 

 ficial resemblance to those of B. typhosus, and as the bacilli do 

 not coagulate milk, produce indol, nor form gas in glucose 

 media, and some varieties are decolorised by Gram's method of 

 staining, it is easy to understand that they might be mistaken 

 for typhoid bacilli if the further tests given under B. typhosus 

 were not carried out. 



The B. fluorescens putridus described by Fliigge is also 

 closely allied to the B. fluorescens non-liquefaciens, but as it is 

 considered by many authorities (Mace, &c.) to be characteristic 

 of foul waters, it has been included under the sewage bacteria. 



The B. erythrosporous and the B. pyocyaneus also produce 

 pigment which gives rise to a greenish fluorescence in media ; 

 these organisms are rarely, if ever, found in pure waters^ and 

 have therefore been included in the sewage group. 



GROUP II. 



This group includes the varieties of the B. aquatilis sulcatus 

 described by Weichselbaum. These bacilli are frequently found 

 in water derived from wells, springs, and rivers. The cultural 

 characteristics of the most common variety are as follows : 



