14 THE UNIVERSITY SCIENCE BULLETIN. 



unpolluted water the number of organisms developing at 37° C. 

 is quite small, being, as a rule, under 50 per cc, while for polluted 

 water the count is high. Too much stress must not be laid upon 

 the count alo'ne, yet one can get some idea as to whether the 

 water is at least clean or dirty by the number of bacteria develop- 

 ing at the body temperature. 



For a long time bacteriologists considered that the character of 

 a water could be determined by the number of bactei'ia developing 

 on agar and gelatine. Eventually bacteriologists realized that the 

 quality or kind of bacteria present, as well as the quantity, is of 

 prime importanc^e. The customary qualitative test made on any 

 sample of water is one to determine whether Bacillus coli is pres- 

 ent, and if so, in what quantity. A test is made for this particular 

 intestinal organism, because if it is present it is easily found and 

 identified, and since it is a normal inhabitant of the colon or large 

 intestines of warm-blooded animals, it indicates, when present in 

 sufficient quantity, i. e., 1 per cc. or more, pollution with animal 

 waste. 



In England, where the sewage is much more concentrated than 

 in America, sewage streptococci are looked for in water examina- 

 tion instead of B. coli. The English argue, with reason, that the 

 sewage streptococci are more delicate than Bacillus coli, and hence 

 their presence in a water is a certain indication of recent sewage 

 pollution. In these examinations streptococci were looked for as 

 well as Bacillus coli. Daniel D. Jackson, in the Journal of Infec- 

 tious Diseases, March, 1907, defines Bacillus coli as a Gram nega- 

 tive organism capable of fermenting both dextrose and lactose, 

 with the production of carbon dioxide and hydrogen, which does 

 not liquefy gelatin in fourteen days and which is morphologically 

 a rod. 



It is a well-known fact that ordinary ox bile has an inhibitive 

 action on the majority of bacteria outside of those belonging to 

 the typhoid and colon groups. Also that comparatively few or- 

 ganisms outside the colon group ferment lactose. Hence lactose 

 bile — ordinary ox bile to which has been added one per cent pep- 

 tone and one per cent lactose — is a medium made use of in ex- 

 amining a water for Bacillus coli. Measured quantities of water 

 are added to fermentation tubes containing lactose bile; and if 

 Bacillus coli is present the lactose will be fermented and carbon 

 dioxide and hydrogen will be given off. When gas showed up in 

 any of the fermentation tubes, confirmatory tests were made to 

 see whether it was B. coli or some other organism that was causing 



