NITROGEN METABOLISM OF BACTERIA 



395 



tubes. The hydrogen ion concentration in these reached a point 

 which inhibited the metabolic activities of the organism. This 

 was apparent from the constancy of the biuret and the Sorensen 

 figures. Proteus vulgaris, like Bacillus coli, was unable to fer- 

 ment 0.4 per cent glucose completely, although 0.2 per cent was 

 utilized in twenty-four hours. 



Lactose was without effect on the protein metabolism of 

 Proteus vulgaris. This was to be expected, of course, as this 

 organism is generally regarded as being unable to attack lac- 

 tose, in spite of a few claims to the contrary. The acidity, 

 biuret and Sorensen figures, and the indol and sugar tests were 

 the same in the lactose broth as in the plain peptone bouillon. 



The above observations strongly indicate that the H ion 

 concentration plays the important role in the inhibition of 

 nitrogen metabolism in a medium containing a fermentable 

 sugar. The failure of certain organisms to attack protein in 

 the presence of carbohydrates is firmly established. That this 

 failure is dependent on a coincident rise in the acidity of the 

 medium is fully supported by the following experiments. 



Media of the same composition as those already described 

 were employed, with and without the addition of dipotassium 

 phosphate. The media were made up as follows: 



B 



Peptone, 0.5 per cent 



Beef extract, 0.25 per 



cent 

 NaCl, 0.5 per cent 



2D 2DP 



1 + 0.2 per cent glucose 2D plus 0.5 per cent 



K2HPO4 



4D 4DP 2L 



B plus 0.4 per cent glu- 4D plus 0.8 per cent B plus 0.2 per cent lac- 

 cose K2HPO4 toss 



2LP 



2L plus 0.5 per cent 

 K2PO4 



B plus 0.4 per cent lac- 

 tose 



4LP 

 4L plus 0.8 per cent 

 K2HPO4 



The dipotassium phosphate was used to serve as a buffer. 

 The organisms employed were Bacillus coli and Proteus vulgaris, 



