CHAPTER X. 



QUALITATIVE ANALYSIS continued. 



SPECIES OF STREPTOCOCCI AND STAPHYLOCOCCI. 



THE value of these organisms as indicative of sewage con- 

 tamination was prominently brought forward by Houston in 

 the supplement to the report of the Local Government Board 

 for 1898-99. Laws and Andrewes, however, in 1894, pointed 

 out that a small streptococcus was the commonest organism 

 present in fresh sewage from St. Bartholomew's Hospital. The 

 colonies of this organism were minute, grew slowly, and possessed 

 the power of coagulating milk in twenty-four to thirty-six 

 hours, when incubated at 37 C. In a specimen of sewage from 

 Snow Hill the same streptococcus was very abundant. An old 

 specimen of sewage from Barking showed numerous colonies of 

 the streptococcus and a yellow staphylococcus, but did not 

 appear to contain any B. coli. This last observation is of the 

 greatest importance in relation to the contamination of potable 

 waters by old sewage. In my own work I have repeatedly 

 examined waters which, from their local surroundings, must 

 have been polluted with sewage, and yet I have been unable 

 to find the slightest traces of B. coli in them ; streptococci 

 were, however, nearly always present. On considering the 

 question, I thought that possibly B. coli died out in sewage 

 kept under the conditions of an old and little-used cesspool ; 

 and on testing the point experimentally I found that B. coli 

 gradually disappeared from many specimens of sewage kept 

 in the dark at the temperature of an outside verandah. But 

 the commonest organisms which persisted in these old specimens 

 of sewage were varieties of streptococci and staphylococci, and I 

 proceeded to examine the cultural reactions of the commonest 

 types of these microbes, believing that their isolation might be 



