332 LIGHT AND THE BEHAVIOR OF ORGANISMS 



It will be seen at once that the effect of different parts 

 of the prismatic solar spectrum on the movement of 

 Amoeba is not proportional to the energy contents, for 

 the energy gradually increases as one proceeds from the 

 violet toward the red end, whereas the region of maximum 

 stimulation for this animal is in the blue, from which it de- 

 creases toward both ends. Nor is it proportional to the 

 brightness as judged by the human eye, for the yellow is 

 much brighter than any other part of the spectrum. In 

 fact, under the conditions of the experiment, one could 

 hardly bear to look through the microscope when the 

 yellow was reflected, while in the case of blue, the region of 

 maximum stimulation for Amoeba, there was no unpleasant 

 stimulation whatever to the eye. 



One of the most interesting characteristics in the re- 

 actions of unicellular forms is the variation in the loca- 

 tion of the region of maximum stimulating efficiency in 

 the spectrum. The experimental results presented above 

 indicate that for the swarm-spores it is in the indigo, for 

 Amoeba it is in the blue, while Oscillaria appears to be 

 stimulated equally by all the visible rays. This indicates 

 that, as in plants so in unicellular forms, the chemical 

 changes associated with the reactions to light are not the 

 same in all of the different species (see p. 320). 



