IX 



Quite recently Makgill 19 ) and Savage 20 ) have used 

 the method for the examination of water. Both authors 

 regard the reaction as a very delicate test for the pre- 

 sence of B. coli and state that a negative result may 

 be relied upon as evidence for the probable absence of 

 the bacillus. Savage agrees with Scheffler, Hunter and 

 Makgill, that the best results are obtained by using 

 glucose agar and recommends VaVo glucose agar to 

 which neutral red has been added. 



Rothberger, Hunter and Makgill found B. Friedlanderi, 

 B. pyocyaneus etc. unable to reduce neutral red, while B. 

 enteritidis of Gaertner and some anaerobic forms (B. 

 tetanus etc.) were able to do so. 



Since the publication of the researches of Roth- 

 berger, Wolff and Scheffler, we have from time to 

 time used this test amongst others for the differen- 

 tiation of B. typhosus and B. coli. As a rule the 

 result was as expected, but occasionally the reaction 

 failed to occur, therefore we concluded that this test 

 was probably just as unreliable as all the others, the 

 serum test perhaps excepted. After the appearance, of 

 the paper by Hunter, whose results were quite in accor- 

 dance with those of Rothberger, we thought it of inte- 

 rest to ascertain why certain strains of B. coli would 

 sometimes produce the reaction and sometimes not, and 

 so possibly make the reaction of Rolhberger more reli- 

 able. - 



The results of these experiments are shortly recorded 

 here by referring to the accompanying tables. 



Ordinary peptone bouillon and agar containing 0.5 

 % of 1 % watery neutral red solution were used for 

 the experiments. Thus the quantity of neutral red em- 

 ployed is exactly the same as that which we found 

 proposed later by Savage. This % was chosen because 



