120 ELEMENTS OF WATER BACTERIOLOGY 



of the red colonies carried out as described for the 

 dextrose-broth method. It has unfortunately proved, 

 however, that with waters of fairly good quality the 

 phenol interferes with the colon bacilli themselves to 

 a serious extent. The dextrose broth furnishes a more 

 delicate test than the carbol broth when the number of 

 colon bacilli present is small, as is clearly shown by the 

 following table from Irons: 



PROPORTION OF POSITIVE RESULTS IN TESTS OF POL- 

 LUTED AND UNPOLLUTED WATERS BY DEXTROSE 

 FERMENTATION-TUBE AND CARBOL-BROTH METHODS 



(Irons, iqoi) 



Dextrose 

 Fermentation- 

 tube. 



Carbol-broth 

 Method. 



Polluted waters 



Relatively unpolluted waters . 



+ - ? 

 33 31 S 



56 38 25 



+ - ? 

 38 30 I 



37 61 21 



The Eijkman Test. Another enrichment test, which 

 has been extensively used in Germany for checking 

 the development of overgrowing forms and limiting 

 the bacteria in the fermentation tube to the colon 

 group, is the Eijkman test, which depends on the use 

 of a high temperature (46°) (Eijkman, 1904). There 

 is no doubt that such a procedure cuts out the water 

 bacteria, and Christian (1905), Neumann (1906), and 

 Thomann (1907) have reported good results from its 

 use. Hilgermann (1909), too, urges the value of the 

 Eijkman test and concludes that the colon-like bacilli, 

 which fail to grow at 46°, are characteristic of compara- 

 tively unpolluted waters. Other observers maintain, 



