124 BACTERIOLOGICAL EXAMINATION OF WATER. 



consisting of six to twenty cocci. On gelatine plates it forms, 

 at first, round, sharply-outlined colonies; later they are dark 

 and surrounded by a broad clear funnel of liquefaction. In 

 gelatine stab there is a funnel-shaped liquefaction. After 

 six to eight days, at the bottom of the completely liquefied 

 gelatine there appears a white, finely granular deposit. On 

 agar there is a scanty surface growth. On potato a scanty 

 growth appears in the form of small white raised points. It 

 grows best at blood-heat, and gas production has not been 

 observed. 



The varieties of streptococci which I have found most 

 commonly in polluted water-supplies correspond to the strepto- 

 coccus B., streptococcus E., and the "sewage streptococcus 11 

 of Houston. In many of the waters which contained these 

 organisms the B. coli was not detected, and an opinion was 

 formed that the waters in question had been polluted with old 

 sewage ; the opinion was usually found to be justified by a local 

 examination of the supply. My experience does not support 

 the contention that streptococci probably indicate a dangerous 

 contamination. As I have already mentioned, the sewage 

 streptococci appear to maintain their vitality in sewage for a 

 much longer time than B. coli. Specimens of barrack sewage 

 preserved in a laboratory cupboard for three months and then 

 diluted 1-100 or 1-1000 with tap-water, show, when examined 

 by the usual methods, large numbers of streptococci but few 

 or no B. coli. Old sewage from which B. coli has disap- 

 peared will be unlikely to present conditions favourable to 

 the prolonged vitality of the B. typhosus or Sp. cholera?. 

 Consequently it appears that streptococci alone cannot be 

 considered as necessarily indicating a dangerous contamina- 

 tion. It is true that when the dilutions of old sewage are 

 kept for a few days the streptococci rapidly disappear ; so 

 their presence in a water-supply undoubtedly indicates a 

 recent contamination, but the contamination is not necessarily 

 dangerous unless the streptococci are accompanied by B. coli. 



