10 K. S. LASHLEY 



With the uncertainty of the discrimination method it seems 

 necessary either to introduce some technique which will elim- 

 inate fluctuations of attention or to test for the relative stimu- 

 lating effects of monochromatic lights when the energy remains 

 constant and only the state of adaptation changes. In testing 

 for the Purkinje phenomenon I did not realize the necessity 

 for avoiding threshold stimuli and so carried out only a few 

 tests with constant light energies. 



Contrary to the statements of Hess the red never seemed 



to have a greater stimulating value than the green of equal 



energy either for the light or for the dark adapted chick. (The 



energy of the red which he used was probably much greater 



than that of the green.) By a series of tests an energy relation 



was determined at which the red was just brighter than the 



green for the light adapted chick. This was at red 1/6, green 



1/45 of the standard. When the energy of the red was decreased 



to 1/18 there was no choice, when it was increased to 2/9 it 



was chosen accurately and without hesitation. With red 650 h/j,, 



intensity 1/6, and green 520 pp, intensity 1/45, Chick C, light 



adapted, chose — 



Red Green 

 11 2 



84% 16% 



He was dark adapted for one hour, then chose- 



Red Green 



4 6 



40% 60% 



Light adapted immediately he chose — 



Red * Green 



3 1 



Chick A under the same condition became erratic, developed 

 a position habit, and gave no results that can be interpreted. 

 The few records of Chick C indicate that there is a shift in the 

 point of greatest stimulating value of the spectrum from the 

 longer to the shorter wave-lengths with increasing darkness 

 adaptation. The number of trials is too small for certainty. 

 As there was the danger of association of one or other color 

 with food work with red and green was dropped at this point 

 and the apparatus was arranged to give yellow 590 pp. and 

 blue-green 500 pp. at equal energies. Both lights were cut 



