86 J. BKONFENBEENNER, M. J. SCHLESINGER AND D. SOLETSKY 



Rosolic acid, however, even in a concentration of 0.005 per 

 cent was markedly inhibitory for many of the organisms tested. 

 Furthermore, this inhibition was almost strictly selective. None 

 of the Gram positive organisms which we tested grew in peptone 

 water containing 0.005 per cent of this dye, and only a few grew 

 to a slight extent when the concentration was one-half of this 

 amount. On the other hand, all the Gram negative organisms 

 which we tested, with the exception of two strains: namely, B. 

 enteritidis "M. N. H. 234" and B. suipestifer "P. D. 48" grew 

 well on a medium containing 0.005 per cent Rosolic acid. 3 The 

 great majority of these forms grew on a medium containing 0.05 

 per cent, and most grew on that containing 0.125 per cent of this 

 dye. Fifteen other strains of B. enteritidis tested by us grew on 

 a medium containing 0.005 per cent of Rosolic acid. Of these, 

 fourteen grew on 0.05 per cent and twelve on 0.125 per cent of 

 Rosolic acid. Four cultures of B. suipestifer grew on 0.125 per 

 cent of Rosolic acid. 



The addition to the medium of both dyes, composing the indi- 

 cator CR, gave practically the same results as those given by 

 Rosolic acid in the same concentration, as might be expected 

 from the inertness of China blue alone. 



These results correspond rather closely to those obtained by 

 Churchman (1912, 1913), and Krumwiede and Pratt (1914) and 

 Kligler (1918) who used various dyes of the triphenylmethane 

 group, such as brilliant green, methyl and crystal violet, etc. 

 However, these workers found that the growth of Bacillus dysen- 

 teriae was almost as readily inhibited by the dyes tested as that 

 of Gram-positive bacteria. Rosolic acid is quite different from 

 the other dyes in that the various strains of Bacillus dysenteriae 



3 The B. enteritidis strains which we used are apparently identical with 

 those used by Churchman (1912, 1913) and Krumwiede and Pratt (1914) in their 

 work on gentian violet and on various green dyes respectively. It is interesting 

 to note that strain "M.N.H. 234" which persistently failed to grow on gentian 

 vio'et and on the green dyes also failed to grow on Rosolic acid. 



