Generic Characters in the Coccaceae 



183 



With nitrate reduction and the optimum temperature for chro- 

 mogenesis the Gram reaction shows no special relations. With 

 optimum growth temperature, on the other hand, Table, 20 shows 

 a distinct connection. As always, most of the cuUures grow equally 

 at both temperatures. Among the decolorized cultures, however, 

 a fair proportion grow best at 20°, while with the positive forms 

 37° is most favorable. Such a relation would, of course, be expected 

 from the generally saprophytic habit of the negative forms. 



The liquefaction of gelatin does not show any distinct relation 

 to the Gram reaction. On the whole, therefore, we may conclude 

 that the cocci which decolorize by Gram are generally earth and 

 water forms, which notably fail to ferment sugars, and which grow 

 best at 20°. The marked correlation with the power of acid pro- 

 duction, in the absence of other equally marked relations, seems 

 to invite further study of the physiological basis of these properties. 



4. Surface Growth. 



The cocci studied were divided into five groups according to the 

 vigor of surface growth on agar. The first group, of "very faint" 

 growths, includes 19; the second group, of "meager" growths, 

 includes 21 forms; "good" and "abundant" growths occur 215 

 and 190 times, respectively; and 55 cocci show "very heaNy" 

 growths. 



TABLE 21. 

 Correlation between Surface Growth and the Fermentation of Dextrose Broth. 



Acidity Produced (Per Cent 

 Normal) 



o and alkaline 



I-0.2 



3-06 



7-2 .0 



o and over . . . 



Very Faint 



Meager 



2 



3 

 II 



4 

 I 



Good 



42 

 4> 

 76 



S3 

 3 



Abundant 



41 

 51 

 54 

 39 

 5 



Very Heavy 



33 



14 

 12 



s 



I 



TABLE 22. 

 Correlation between Surface Growth and the Fermentation of Lactose Broth. 



Acidity Produced (Per Cent 

 Normal) 



-0.2 and more alkaline 



— o . I and 0.0 



o. 1-0.4 



0.5-1.4 



1 . 5 and over 



Abundant \'ery Heav-y 



5 



30 



It 



8 



I 



