165 



earlier, much employed reaction of Kitasato-Salkowski should, 

 according to statements in the literature, be given up). 



y(C 6 H 4 )\ ,H 



(NH)( C* - (CH 2 ) - C( - NH 2 



\ (CH) / MCO) OH 



In certain cases bacteria can elaborate indol from open 

 chains (Logie), but usually the only essential for indol for- 

 mation is the presence in the medium of tryptophane or com- 

 plexes from which it can easily be split off. 



We must, on the whole, undoubtedly agree with M. Neisser 

 that the presence or absence of the power to form indol is 

 one of the most constant biological characters of bacteria. He 

 says: „wir mussen deshalb die bakteriologische Identitat ohne 

 sachgemasse Anstellung der Indolreaktion fur unvollstandig er- 

 klaren". 



As it soon appeared that there were both indolpositive 

 (that is indol-producers) and indol-negative strains in the Pfeif- 

 fer's bacillus group, it was necessary to investigate whether, 

 on the basis of this property, Pfeiffer's bacillus might be separa- 

 ted into two sharply-defined groups. To decide this we must 

 know: (1) whether any sharp boundary can be drawn between 

 the positive and negative indol reactions; (2) whether an indivi- 

 dual strain is constantly indol-positive or indol-negative; (3) 

 whether any connection can be demonstrated between the 

 grouping of the strains according to the indol test and their 

 other biological characters. 



The results of my indol tests will first be reported in 

 tabular form, and then the necessary explanations and comments, 

 together with some supplementary investigations will be given. 



