226 SA CTEBIOL G Y. 



lihood of its presence being masked by other color- 

 reactions. 



Muir and Ritchie recommend the use of ordinary 

 fuming or yellow nitric acid for this test. In this 

 method two or three drops of the acid are added to 

 the culture under consideration. If indol be present, 

 the red color appears as a result of the reducing action 

 of the nitrous acid upon it. The defect in this method 

 is that it reveals only the presence of indol, and ^ails to 

 indicate whether or not reducing-bodies were coinci- 

 dently formed with the indol. As a test for indol alone 

 it is convenient and entirely trustworthy. 



Tests for nitrites. For this purpose Lunkewicz rec- 

 ommends the employment of Ilosvay's modification of 

 the method of Griess. As reagents the following solu- 

 tions are employed : 



u. Naplithylamine . . . . 0.1 gramme. 



Distilled water .... 20.0 c.c. 



Acetic acid (25 per cent, sol.) . . . 150.0 c.c. 



S. Sulfanilic acid . . . 0.5 gramme. 



Acetic acid (25 per cent, sol.) . . 150.0 c.c. 



In preparing solution a the naphthylamine is dis- 

 solved in 20 c.c. of boiling water, filtered, allowed to 

 cool, and mixed with the dilute acetic acid. Solutions 

 a and b are then mixed. The resulting mixture should 

 be colorless. It is best to prepare it as needed, though 

 if kept in a closely stoppered flask it retains its virtues 

 for some time. 



When added to cultures containing nitrites, in the 

 proportion of one volume of reagent to five volumes 

 of the culture, a deep-red color appears in a few 

 seconds. If no nitrites are present, no color-reaction 

 occurs. In testing cultures always control the results 



