SELIG HECHT 



383 



It requires the least amount of energy to produce a given photosensory 

 effect. 



2. It will be of significance to determine quantitatively the relative 

 effectiveness of the different parts of the spectrum. The method used 

 in this connection deserves a little consideration. It is required to find 

 the relative effectiveness of a series of reagents on a given system. 

 The common procedure of comparing the different effects produced 

 by the same concentration of the reagents, though giving qualitative 

 results, is utterly fallacious for quantitative purposes, except in rare 

 instances such as when the effect produced is a linear function of the 



O /.O ZO 3.0 -*<? 



logarithm of inteosifj^ 



Fig. 4. /Msochromes for the responses of Mya to the different lights transmitted 

 by the various filters. 



concentration. A quantitatively correct evaluation requires the com- 

 parison of the concentrations of the different reagents which will 

 produce the same effect. 



I need not labor the point, because Brooks (1920) has presented it 

 in some detail in its bearing on the theoretical interpretation of 

 hemolysis data. Applied to our immediate problem, it follows that 

 the important thing in working with spectral light is not to have a 

 spectrum of equal energy distribution with which to determine the 

 relative effects of different parts of it, but to have a spectrum of 

 variable, known energy distribution, with which to determine the 



