100 THE NATURE OF ANIMAL LIGHT 



teritmi phosphor escens , was a facultative anaerobe and 

 would grow, i.e., multiply, but not luminesce in the absence 

 of oxygen. Some forms, ordinarily producing light, will 

 grow, but fail to luminesce at high temperatures. Bei- 

 jerinck (1915) has recently found that these individuals 

 may, by continued cultivation at high temperatures, form 

 non-luminous strains which fail to luminesce when again 

 brought into lower temperatures, favorable for lumines- 

 cence. These non-luminous mutants occasionally give rise 

 to atavistic brilliantly luminous forms. Beijerinck also 

 finds that after exposure of Photohacter splendidum to 

 ultra-violet or strong sunlight, radium or mesothorium 

 rays, luminescence continues but no growth occurs. There 

 is thus ample evidence that growth and respiration are 

 properties quite distinct and separable from luminescence. 

 Indeed, respiration increases continuously up to a rela- 

 tively high maximum whereas luminescence falls off rap- 

 idly above a relatively low optimum. McKenny (1902) 

 found also that Bacillus phosphor escens could grow rap- 

 idly in 0.5 per cent, ether without producing light. 



Luminescence has been compared in bacteria to pig- 

 ment formation, as rather definite cultural conditions are 

 necessary for realization of both chromogenic and photo- 

 genic function. Some pigment-formers, as Bacillus pyo- 

 cyaneus, which produces a water-soluble green pigment, 

 remain colorless under anaerobic conditions. A colorless 

 chromogen is formed, which oxidizes to the green pigment 

 in the air. If this colorless chromogen produced light 

 during its oxidation as well as green pigment, we would 

 have a case of both chromogenic and photogenic function 

 combined in one species of bacterium. Luminescence in- 



