8 4 



RELATIONSHIPS OF THE COCCACE^E 



The correlations between chromogenesis and the fer- 

 mentation of the sugars are singularly perfect. The white 

 forms in each case show two maxima, one corresponding 

 to the true white chromogens, the second, at a higher 

 acidity, to the colorless streptococci. The latter include 

 a majority of the strongest acid-producers in each sugar. 

 The other types show for each sugar a regular and charac- 

 teristic curve, as indicated for dextrose in Figure II. The 

 yellow forms show a mode at the neutral point. The 

 orange chromogens, on the other hand, produce most 

 commonly an intermediate grade of acidity, 0.3 to 0.6 

 per cent acidity in dextrose broth, and 0.1 to 0.4 per cent 

 in lactose broth. The red forms show the same relation 

 as the orange forms toward dextrose, while in lactose 

 broth they resemble the yellow chromogens, producing 

 in most cases no change in reaction. 



CORRELATION BETWEEN CHROMOGENESIS AND NITRATE 

 REDUCTION. 



Number of cultures in each class. 



With regard to the reduction of nitrates, the white 

 forms show generally negative results. Nitrites are pro- 

 duced by only one in ten of the yellows, and by a slightly 

 higher fraction of the orange forms, but by half the red- 



