536 PAUL R. CANNON 



Tubes of media prepared in this way were inoculated with 

 known indol-forming bacteria, and, at the end of eighteen hours, 

 the indol test was made by using p-dimethyl-amido-benzaldehyde. 

 A pronounced red color almost instantly appeared, showing the 

 presence of indol. The control and non-indol-formers remained a 

 straw color after the addition of the aldehyde. It proved un- 

 necessary in my tests to use amyl alcohol to dissolve out the 

 color, although this may be done in case indol formation is 

 doubtful. 



The brief time — eighteen to twenty-four hours — necessary for 

 the test by the above method, is a great improvement over the 

 old standard peptone test, which required five days. Further- 

 more, hydrolyzed casein can easily be obtained or prepared, and 

 the constituents of the inorganic solution are available in most 

 laboratories. 



REFERENCE 

 (1) Zipfel: Centralblatt f. Bakt., etc., Orig. Abt. 1, 64, 65, 1912. 



