86 



RELATIONSHIPS OF THE COCCACE^ 



CORRELATION BETWEEN CHROMOGENESIS AND GELATIN 



LIQUEFACTION. 



Number of cultures in each class. 



The liquefaction of gelatin presents another correlation 

 with pigment production. The white and red forms are 

 almost all non-liquefiers ; the yellow cocci show a maximum 

 among the moderate liquefiers; and the orange chromo- 

 gens exhibit the peptonizing power to a high degree. 



It is clear, therefore, that there exist among the cocci 

 four (or five) distinct groups marked by characteristic 

 pigment production, each group being also denned by a 

 number of other correlated characters. The "white" 

 forms generally stain by Gram, fail to reduce nitrates, 

 grow well at 37 degrees, and usually fail to liquefy gelatin. 

 They include two subgroups — the feebly -growing, 

 strongly acid-producing forms, which are really colorless, 

 not white, and the white-pigment-producers, which grow 

 abundantly and produce a moderate amount of acid. 

 The "yellow" chromogens frequently show packets, are 

 usually Gram-negative, give a good to a very heavy sur- 

 face growth, produce little or no acid, grow well at 20 

 degrees, and show a moderate liquefaction of gelatin. 

 The "orange" pigment formers stain well by Gram, 



