202 ELEMENTS OF WATER BACTERIOLOGY 



short chains, or irregular groups. They do not show 

 visible growth and do not form indol and nitrite 

 in the standard peptone and nitrate solutions; most 

 of them do not liquefy gelatin, though occasionally 

 forms are found which possess this power. Until recently 

 no systematic study of the various species found in the 

 intestine had been made and all cocci giving the char- 

 acteristic growth on agar and strongly fermenting 

 lactose are commonly included as " sewage streptococci." 

 Although the significance of the streptococci as sewage 

 organisms is not established with the same defmiteness 

 which marks our knowledge of the colon group, these 

 forms have been isolated so frequently from polluted 

 sources and so rarely from normal ones that it now seems 

 reasonable to regard their presence as indicative of 

 pollution. Although originally reported by Laws and 

 Andrewes (Laws and Andrewes, 1894), their importance 

 was not emphasized until 1899 and 1900, when Hous- 

 ton (Houston, i899 b , i9Oo b ) laid special stress upon 

 the fact that streptococci and staphylococci seem to 

 be characteristic of sewage and animal waste, the former 

 being, in his opinion, the more truly indicative of 

 dangerous pollution, since they are " readily demon- 

 strable in waters recently polluted and seemingly 

 altogether absent from waters above suspicion of con- 

 tamination." In six rivers recently extensively sewage- 

 polluted, he found streptococci in from one-tenth to 

 one ten-thousandth of a c.c. of the water examined, 

 although in some cases the chemical analysis would not 

 have indicated dangerous pollution. On the other 

 hand, eight rivers, not extensively polluted, showed 



