On the other hand, it is very easy to prove that luminescence, even in bacteria, is not connected with respiration. Thus, Beijerinck (1889 _c_) found that of several species of luminous bacteria studied by him, one, _Bacterium phosphorescens_, was a facultative anaërobe 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. Beijerinck (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 luminescence. These non-luminous mutants occasionally give rise to atavistic brilliantly luminous forms. Beijerinck also finds that after exposure of _Photobacter 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 relatively high maximum whereas luminescence falls off rapidly above a relatively low optimum. McKenney (1902) found also that _Bacillus phosphorescens_ could grow rapidly in 0.5 per cent. ether without producing light. Luminescence has been compared in bacteria to pigment formation, as rather definite cultural conditions are necessary for realization of both chromogenic and photogenic function. Some pigment-formers, as _Bacillus pyocyaneus_, which produces a water-soluble green pigment, remain colorless under anaërobic 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 involves something more than respiration, an oxidation of a very definite and particular kind.