122 BACTERIOLOGICAL EXAMINATION OF WATER. 



Houston also isolated seven other varieties of streptococci 

 from " soil-washings " which were characterised by colonies with 

 clean edges. The broth cultures were clear, with a deposit at 

 the bottom of the tube. Four of the organisms produced 

 strong acidity but no clotting in milk. None of the cultures 

 showed pyogenic or pathogenic properties. 



In the third Report to the London County Council on the 

 Bacterial Treatment of Crude Sewage, Houston stated that the 

 type of streptococcus most abundant in sewage presented the 

 following characteristics : 



Sewage Streptococcus (Houston). 



Source. Barking and Crossness crude sewage and effluents 

 from bacterial coke-beds. 



Abundance. Usually more than 1000 per c.c. of crude 

 sewage and effluents. 



Temperature. Grows well at blood heat. 



Morphology. Stains well by Gram's method. The chains of 

 cocci are usually short. 



Agar and Gelatine-plate Cultures. The colonies are small and 

 transparent. They are nearly circular in shape with a clean 

 edge. The granulation is faint. The colonies in agar are 

 usually more granular and darker-looking than in gelatine 

 cultures. The gelatine is not liquefied. 



Streak Cultures. (Agar at 37 C. and gelatine at 20 C.) 

 The growth usually shows itself as a delicate white film, which 

 on close observation is seen to be made up of numerous separate 

 minute transparent-looking colonies. The gelatine is not lique- 

 fied. 



Broth Cultures (37 C.). Abundant diffuse cloudiness. On 

 gently shaking the tube a viscous white deposit rises from the 

 foot of the tube in a spiral form. 



Litmus-mill: Cultures (37 C.). Acidity, but usually no clot. 



Roscoe and Lunt isolated from sewage a streptococcus, which 

 appears closely allied to the varieties I have already described. 

 The cultural characteristics of this organism are as follows : 



Streptococcus Mirabilis (Roscoe and Lunt). 



Gelatine Plates. It grows badly. The colonies in the depth 

 of the gelatine after four days incubation are mere dots or 



