INDOL PRODUCTION BY BACTERIA 475 



any considerable number of strains of an organism in group II 

 have been examined, negative as well as positive results have 

 been reported, with the exception of the cholera vibrio. 



From this summary we must conclude that whereas the indol 

 test may serve as a valuable aid in differentiating bacteria, it 

 cannot be regarded as an absolute criterion. A positive test may 

 give definite information but a negative test must be interpreted 

 with caution. 



We should also like to emphasize the necessity for a standard 

 reagent for the indol test and suggest the use of Ehrlich's 

 dimethylamidobenzaldehyde solution for this purpose. 



In this table we have used the classification adopted by the 

 Society of American Bacteriologists (Winslow, 1920). 



Group I. Indol negative 



Bcaillus anthracis* (Zipfel) 



subtilis* 

 Actinomyces asteroides* 

 bovis* 

 graminaris* 

 Bacterium abortum (Weeter) 



cloacae (5 strains*, Kligler) 



enteritidis (3 strains*, Crossonini, Porcher and Panisset, Zipfel, 



Nonnotte and Demanche) 

 fecalis-alcaligenes (3 strains*) 

 icteroides (Crossonini) 

 mucosum-capsulatum* (Hiss and Zinsser) 



paratyphosum A (2 strains*, Zipfel, Jordan, Nonnotte and Demanche) 

 paratyphosum B (13 strains*, Zipfel, Jordan, Nonnotte and Demanche) 

 pullorum (5 strains*, Mulsow) 

 rhinoscleromatis* 

 sanguinarium (Mulsow) 

 suipestifer (4 strains*, Zipfel, Crossonini) 

 typhosum (15 strains*, all investigators) 

 typhi-murium (Nonnotte and Demanche) 

 Clostridium botulinum (6 strains*) 

 chauvei* 

 Welchii* 

 Corynebacterium Hoffmannii (3 stains*) 



pseudodiphtheriae (4 strains*) 

 xerosis (2 strains*) 



* Our tests. 



