COMPARATIVE STUDY OF THE COCCI 59 



and moisture in the tube. Faint growths are moist and 

 shining, while heavy growths in tubes which do not 

 contain much moisture show the dry, rough, dull appear- 

 ance. The " white chromogens" showed another differ- 

 ence, varying from an opaque porcelain-white to a duller 

 and more translucent growth, of indefinite color and 

 somewhat shiny appearance. The latter type of growth 

 was distinctly viscid to the needle. 



We noted, as cultural characters on the agar streak, 

 the color production and the vigor of surface growth. 

 The method of studying the former character will be 

 described under " Chromogenesis. " Under "Vigor of 

 Surface Growth" we distinguished five different types. 

 Grade 1 includes forms like the Streptococcus which 

 form only a very faint, veil-like growth or a few trans- 

 lucent dotted colonies on the surface. Grade 2 is reserved 

 for a somewhat more abundant, but still meager growth. 

 Grade 3 corresponds to a good but not abundant streak; 

 Grade 4 to an abundant growth; and Grade 5 to a very 

 heavy surface development. 



The response to free oxygen is directly related to the 

 vigor of surface growth; the streptococci, which form only 

 a faint film on the surface, grow fairly well in the stab ; 

 and conversely the sarcinae, which form abundant surface 

 masses, grow badly in the stab. The agar streak and 

 stab culture, therefore, distinguish in a general way 

 the semi-anaerobic from the strongly aerobic forms. 

 Inhibition of growth by acidity and alkalinity of media, 



