42 ELEMENTS OF WATER BACTERIOLOGY 



special 20-degree incubator which is difficult to regulate. 

 The 37-degree incubator must be provided in any case 

 for the isolation of B. coli. On the other hand, the 

 time seems hardly ripe for the abandonment of the 

 20-degree count, which has been used for 20 years all 

 over the civilized world, and for the interpretation of 

 which we have very complete data. There is at present 

 no such sound basis for interpreting the 37-degree 

 count, and in many cases, as in the control of water 

 filtration plants, the 37-degree numbers are too small 

 to be of any practical value. Furthermore the 20- 

 degree count may furnish evidence of surface con- 

 tamination as distinguished from fecal pollution, which 

 is often of considerable value. 



The authors have always urged the use of the 37- 

 degree count along with the 20-degree count as furnish- 

 ing most valuable information ; but this is very different 

 from the substitution of one count for the other. 

 The recommendation that the 20-degree count be 

 abandoned, with no evidence to warrant such a revolu- 

 tionary change, and no experimental results on which 

 to base an interpretation of the 37-degree count, has 

 aroused vigorous opposition from a large majority 

 of practical water bacteriologists. At the Washington 

 meeting of the American Public Health Association 

 in September, 191 2, it was resolved " that in the opinion 

 of the Laboratory Section of the American Public 

 Health Association, ordinary routine examination of 

 water for sanitary purposes, and in the control of 

 purification plants, for the present should include the 

 determination of the number of bacteria developing 



