E. NEWTON HARVEY 11 



The maximum wavelength changes from 500 to 470 milhmicrons as 

 the suspension density changes from 40 to 8 arbitrary units. 



The various species of luminous bacteria do possess different maxima 

 in the blue region when measured in dilute suspension (Spruit- van 

 der Burg, 1950). The light of luminous bacteria looks green to the 

 eye when the intensity is sufficiently high to involve color vision, no 

 doubt because the spectral energy curve is skewed, with greatest 

 energy on the long-wavelengths side of the maximum around 480 

 millimicrons. In this respect bacterial luminescence differs from that 

 of the blue Ci/pridina luminescence, whose maximum emission is 

 about 480 millimicrons, but the spectral energy curve is more narrow 

 and symmetrical. Because of the above considerations, bioluminescent 

 emission spectra are not too significant. Nevertheless, as a guide to 

 previous investigations, the measured maximum wavelengths and the 

 reported color of the light of various groups have been collected in 

 Table I, column 9. 



It would be ideal if luminous groups could be separated on the 

 basis of the chemiluminescent systems involved, primarily depending 

 on the structure of luciferin. At the present time that is not pos- 

 sible, but certain organisms can be classed together with reasonable 

 certainty on the basis of similar chemical behavior. There is little 

 doubt but that the fungi and the bacteria contain similar luminescent 

 systems, although the role of flavins in fungal luminescence is as 

 yet not demonstrated. 



So little is known of the biochemistry of luminescence of the Pro- 

 tozoa that it is very difficult to predict a similarity with any of the 

 known chemiluminescent systems. Noctiluca and smaller forms can 

 often be obtained in enormous numbers and should offer good material 

 for chemical research, except that the percentage of luminous sub- 

 stance is undoubtedly small. In Noctiluco, light is always associated 

 with minute granules, which flash on stimulation and emit a steady 

 glow under conditions of injury to the cell. No form is better adapted 

 for cell physiological studies, particularly of the excitation process. 

 Noctiluca is an ideal organism for the investigation of the all-or-none 

 law, time relations of the flash, repetitive stimulation, fatigue, conduc- 

 tion of local excitation, etc., in a single cell. Among other advantages, 

 Noctiluca is large and nearly spherical, 0.5-1.0 mm in diameter, pos- 



