160 ELEMENTS OP WATER BACTERIOLOGY 



RATIO OF TOTAL BACTERIA TO COLON BACILLI IN 

 WATERS OF DIFFERENT CLASSES 



The rather regular decrease in the ratio of the total 

 count to the B. coli count with an increase in the actual 

 number of colon bacilli is very interesting. 



Prof. Gartner apparently holds that this fall in the 

 ratio of the plate count to the " coli titer " indicates a 

 fallacy in the method of the latter and in particular he 

 emphasizes the absurdity of the lowest figures in the table 

 which indicates that there were twice as many colon 

 bacilli as bacteria of all sorts. It seems to us that the 

 last phenomenon is quite as likely to be due to an error in 

 the plate count as to a failure in the enrichment pro- 

 cedure. Unless dilutions are very carefully made 

 plates inoculated with waters containing tens and 

 hundreds of thousands of bacteria per c.c. are pretty 

 likely to be so crowded that only a portion of the bac- 

 teria with which they are sown are able to develop. 

 As to the diminishing ratio with increasing coli-content, 

 it is exactly what might reasonably be expected. One- 

 tenth to one-quarter of the bacteria in sewage may be 



