100 ELEMENTS OF WATER BACTERIOLOGY. 



microscope as cocci, occurring as a rule in pairs, short 

 chains, or irregular groups. They do not show visible 

 growth in the standard peptone and nitrate solutions; 

 most of them do not liquefy gelatin, though occasion- 

 ally forms are found which possess this power. No sys- 

 tematic study of the various species found in the intes- 

 tine has so far been made, and at present all cocci giving 

 the characteristic growth on agar and strongly fermenting 

 lactose may be included as " sewage streptococci." 



Although the significance of the streptococci as sewage 

 organisms is not established with the same definiteness 

 which marks our knowledge of the colon group, these 

 organisms have been isolated so frequently and with such 

 constant results that it now seems reasonable to regard 

 their presence as indicative of pollution. Although orig- 

 inally reported by Laws and Andrewes (Laws and 

 Andre wes, 1894), their importance was not emphasized 

 until 1899 and 1900, when Houston (Houston, i899 b , 

 i9co 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 demonstrable in w-aters recently polluted and 

 seemingly altogether absent from waters above suspicion 

 of contamination." In the water of 6 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 

 did not clearly indicate dangerous pollution. On the 



