SUBFAMILIES AND GENERA OF COCCACE^ 93 



recognized by their characteristic morphology, meager 

 growth on artificial culture media, and typically parasitic 

 habit. Common serum reactions, too, show the close 

 mutual relationships of the members of this group; but 

 the conception of the genus is made much clearer by the 

 comparison of the biochemical powers of these organisms, 

 with those of other cocci. In our original series of 500, 

 only 17 organisms were included which formed the faint, 

 veil-like surface growth of the streptococci. Even this 

 small number of strains sufficed to show that these bacteria 

 exhibit the generally positive Gram reaction of the Para- 

 coccaceae, but differ from the other members of the group 

 in three points. They very rarely liquefy gelatin, and 

 apparently never reduce nitrates, but exert an exception- 

 ally powerful action on dextrose and lactose. We have 

 since examined 44 more cultures of streptococci, making 

 a total of 61 in all. The average acid production for the 

 whole series was .019 normal in dextrose broth and .014 

 normal in lactose broth. These figures are more than 

 twice as high as those obtained for any other genus of 

 the Coccaceae in our investigation. It is important to 

 notice, however, that these averages are composed in 

 each case of two subordinate types within the genus. 

 The actual distribution of the acidities in dextrose broth 

 is plotted in diagrammatic form in Figure II, and it is 

 there apparent that the curve for this genus has two 

 distinct modes, one at an acidity between the neutral point 

 and .004, the other between .010 and .014 normal. It is the 



