506 ALFRED O. GROSS 



5. DISCUSSION 



The results of these experiments with Hghts of measured inten- 

 sity demonstrate conclusively that the effectiveness of the dif- 

 ferent colors of the spectrum does not correspond to the relative 

 intensity of luminosity of the lights, as Merejkowsky ('81) has 

 stated, but to their specific quality. Merejkowsky 's method of 

 equalizing the intensity of the lights, by judging the relative 

 luminosity with his own eye, is very inaccurate, because the 

 different colors of the spectrum have an effect on the eye which 

 is not proportional to their energy content. Furthermore, the 

 maximum brightness of the spectrum differs with different degrees 

 of illumination as is well known from the Purkinje phenomenon. 

 In the bright spectrum the region of greatest luminosity lies in 

 the yellow, in a spectrum from a weaker source, it is in the green. 

 Merejkowsky's results, therefore, cannot be considered seriously 

 as opposing the view, that the efficiency of the different colors 

 of the spectrum to stimulate the lower animals, is independent 

 of intensity. 



The view of Hess ('10) that the relative attractive power of 

 the different homogenous lights approaches or corresponds with 

 the brightness curve of the color-blind person, is not funda- 

 mentally different from the view held by Merejkowsky. Hess 

 has shown, contrary to Loeb's hypothesis, that the reactions of 

 animals are not the same as those of plants in their response to 

 the spectrum, but he has not proven that the yellow and green 

 have the greatest stimulating efficiency when the factor of inten- 

 sity is eliminated. His experiments show that the yellow and 

 green are more efficient than the orange and red of the spectrum, 

 since the latter contain a much greater amount of radiant energy. 

 As the yellow-green rays contain much more energy than the 

 blue and violet, the seemingly greater effectiveness of the yellow- 

 green raj^s is probably due to the greater energy of this region 

 of the spectrum. The results of the experiments by Bert ('68) 

 and by Lubbock ('81, '83) upon the reactions of Daphnia to the 

 spectrum are similar to those obtained by Hess, but unfortu- 

 nately these investigators also ignored the factor of intensity. 



