COMPARATIVE STUDY OF THE COCCI 67 



Pigment formation. The production of color by the 

 bacteria is not only markedly affected by contempo- 

 raneous conditions of cultivation, but may be profoundly 

 modified by selective action or by the effect of antecedent 

 environment. Among the conditions which temporarily 

 affect the production of color, without modifying the 

 inherent chromogenic power of the organism, may be 

 mentioned the medium, the presence of free oxygen, and 

 the temperature. With some bacteria, media of low 

 nutritive value, like potato and Nahrstoff, appear to 

 favor pigment formation, but with the cocci this is not 

 generally the case. Agar has, on the whole, shown a 

 better development of chromogenesis than any other 

 medium tested. The presence of free oxygen is gener- 

 ally an essential for color production, stab growths being 

 almost invariably lightly colored. We found a single 

 exception to this rule in a coccus which produces a 

 reddish pigment of much deeper tint in the stab than 

 on the surface. In comparing color at different temper- 

 atures we found, in general, a much better pigment 

 formation at 20 degrees than at 37 degrees. A deep 

 orange growth at the lower temperature may correspond 

 to a white one at 37 degrees. The relative color pro- 

 duction at 20 and 37 degrees was recorded in our routine 

 studies, and will be more fully discussed later. Besides 

 these temporary modifications of the chromogenic power, 

 the actual color of cultures may be indirectly affected 

 by certain other factors. The general vigor of growth 



