230 ELEMENTS OF WATER BACTERIOLOGY 



what less extensive series of tests, including aerobic 

 and anaerobic counts, both at 20 and 37, with the 

 determination of the number of liquefiers and the num- 

 ber of spore-formers. The results attained do not 

 seem to warrant any such elaborate procedure. As 

 far as the authors are aware, the determination of 

 liquefying bacteria, anaerobic bacteria and thermophilic 

 bacteria does not add any information of material 

 importance to that obtained from the total count. 

 Some test for specific sewage organisms is of course 

 desirable. Here again, however, the determination 

 of B. sporogenes and sewage streptococci tells the 

 observer little more than can be learned from the routine 

 use of the colon test. In the United States the practise 

 of sewage bacteriologists is crystallizing around the 

 total count and the estimation of B. coli. In the absence 

 of evidence as to the specific value of other data, the 

 routine control of filter plants may well be limited 

 to these two determinations. 



The total count of bacteria should be made, as in 

 the case of waters, at 20. Determinations carried 

 out in duplicate at 37 give additional information of 

 considerable value. The ratio of the 37 count to the 

 20 count varies with different sewages. At Boston 

 the body temperature count is 70 to 80 per cent of 

 the total count; at Lawrence it appears to be propor- 

 tionately much lower (Gage, 1906). In using either 

 medium, it is well to add lactose and litmus and note 

 the number of red colonies, as a check on the enumera- 

 tion of B. coli. 



It should be borne in mind, as Lederer and Bach- 



