Ehrlich and Salkowski Tests. 



13 



representing the various members of the colon-typhoid group, were 

 used. Duplicate peptone broth tubes of each strain were in- 

 cubated at 37 0 C. for four days. The contents of the tubes was 

 then divided in half and the half portions subjected respectively 

 to the two tests. 



Twenty-eight of the seventy-five strains were positive in both 

 duplicate tubes with both tests. Thirty-seven were uniformly 

 negative with both tests. Five were positive in both controls 

 with the Ehrlich test and positive in one tube and negative in the 

 other with the Salkowski. Finally five tubes were uniformly 

 positive with the Salkowski and negative with the Ehrlich test. 

 The five cases in which the Salkowski test was positive and the 

 Ehrlich test negative illustrate the fact brought out by Bohme 

 and Marshall that the Salkowski test may give erroneously positive 

 results when indol is not present. This error seems to be due to 

 some red substance other than nitroso-indol but which may easily 

 be mistaken for it. If the test is carefully performed this redden- 

 ing can, however, easily be distinguished from the nitroso-indol 

 red by the fact that it diffuses rapidly throughout the entire tube 

 instead of remaining as a ring between the two liquids. This 

 characteristic coloration was obtained in all those cases which 

 gave repeated negative results with the Ehrlich test, and unlike 

 the nitroso-indol red it was found to be insoluble in chloroform. 

 The five other aberrant results in which the Ehrlich test was posi- 

 tive and the Salkowski test positive in one tube and negative in 

 the other illustrate the possibility of an error in the other direction. 

 I am inclined to think that the negative Salkowski tests in this 

 case were perhaps due to a rapid oxidation of the red coloring 

 matter. On the whole it is quite evident that the Ehrlich test 

 is the more reliable of the two and should displace the other. 



An interesting phenomenon in connection with the Ehrlich 

 test, first called attention to by Seidelin, was also observed by me. 

 This consists in the appearance of a purple to blue color, on the 

 addition of the reagents, which unlike the indol red is insoluble 

 in chloroform. Lewis, working with Seidelin, attributes a special 

 significance to this reaction and reports three distinct colorations : 

 r. Soluble and insoluble red. 



2. Soluble red and insoluble purple or blue. 



3. No soluble red but insoluble blue or purple. 



