116 BACTERIOLOGICAL EXAMINATION OF WATER. 



of great service in solving the difficult problem of sewage con- 

 tamination. The following are the chief types observed up to 

 the present time : 



Streptococcus A. 



Gelatine Plates. The surface colonies were extremely small, 

 with an irregular margin, from which here and there "streamers'" 

 ran out over the surface of the gelatine. An "impression" 

 preparation showed that the colony consisted of small cocci 

 tightly packed together at the centre, but forming short and 

 long chains at the periphery. The gelatine was not liquefied. 



Agar-slope. The growth consisted of numerous small isolated 

 colonies with a circular outline and granular centre. 



Gelatine-stab. On the surface there was a very small circum- 

 scribed film, and a fine thin growth along the stab consisting of 

 small colonies massed together. The gelatine was not liquefied. 



Mill:. Clotted after six days incubation at 37 C. 



Litmus-whey. Faintly acid after twenty-four hours incubation 



at 37 C. The acidity required I'l c.c. per cent, of ^ alkali 

 to neutralise it. After seven days incubation the acidity equalled 

 2 '4 per cent. ^ alkali. 



Broth. After twenty -four hours incubation at 37 C. a diffuse 

 growth appeared with a slight deposit. After ten days the 

 broth was not clear. 



Peptone and Salt Solution. After seven days incubation at 

 37 C. no indol was produced. 



Glucose-gelatine. No gas formation. 



Gelatine (ordinary stab) at 37 C. A diffused growth and 

 slight deposit. 



Potato. Moist glistening surface ; growth hardly apparent. 

 A portion examined under the microscope showed small cocci 

 in chains and masses. 



Microscopical Characters. A twenty-four-hour broth culture 

 showed medium-sized cocci arranged in short chains and small 

 masses. 



Staining Reactions. Stains with basic aniline dyes and by 

 Gram's method. 



