520 KINETICS OF BIOLUMINESCENT REACTION. I 



Photographic methods for the study of various bioluminescences 

 have been developed by several investigators. Friedberger and 

 Doepner^ employed a photographic method of determining the 

 intensity of the light coming from a culture of luminous bacteria. 

 They impressed upon their plates a calibration exposure made with a 

 standard lamp of known intensity, and evaluated the densities with 

 the Martens polarization photometer. It would appear that they 

 did not attempt to control the quantity of their calibration light 

 source so as to match that of the organic luminescence in question. 

 Probably the most careful and important use of photographic pho- 

 tometry in such a study is the work of Ives and Coblentz^ who worked 

 out the spectral energy curve for the firefly, evaluating the intensities 

 along the spectrum by comparing the photographic densities produced 

 by the light of the animal with the photographic effects of a carbon 

 glow lamp, whose spectral energy distribution had been accurately 

 determined. 



In the present investigation I have used throughout Eastman 

 cine-negative motion picture film. The spectral sensitivity of this 

 film extends to about X = 0.59^. This film was obtained from the 

 company before perforation so that the whole width of the film is 

 available for use. The variation in density from point to point in 

 a film, produced by identical exposures, is somewhat less than in 

 plates, in which emulsions are liable to greater variations in thickness. 

 The Eastman laboratories have informed me that the variations to 

 be expected in the developed densities of this film are an average of 

 3 per cent, and an extreme of 6 per cent. Intensity values calcu- 

 lated from such density readings will vary by somewhat higher 

 percentages. Such deviations are of course unfortunate, but represent 

 a difficulty inherent in all methods of photographic photometry. 

 It must be recognized that great precision is not possible with any 

 photographic method. In the present work I have been able to 

 assure myself that I was working well within the expected error of 

 the film; all records have indicated that this was the case. Every 



^ Friedberger, E., and Doepner, H., Centr. Baki., He Aht., Orig., 1907, xliii,l. 



^Ives, H. E., and Coblentz, W W., Luminous efiiciency of the firefly. Bull. 

 Bureau of Standards, 1909, vi, 321. Also see Coblentz, W. W,, A physical study 

 of the firefly, Carnegie Inst. Washington, Pub. No. 164, 1912. 



