UNICELLULAR FORMS AND COLOR 331 



effect described above it is necessary (i) to have amoebae 

 in a certain condition, (2) to keep them in as low light 

 intensity as possible before exposing, and (3) to use very 

 intense light. When exposed in blue after having become 

 active in any other color or in diffuse sunlight, all move- 

 ment stopped instantly in nearly all specimens observed. 

 But there was no apparent contraction; the animals re- 

 tained almost the exact form they had before the exposure. 

 After remaining quiet a few seconds, the streaming of the 

 protoplasm in the anterior pseudopods slowly began again, 

 but now it nearly always proceeded in the same direction. 

 Gradually new pseudopods were formed, usually at the 

 posterior end, and as these developed the old ones were 

 slowly withdrawn. The rate of movement ordinarily in- 

 creased at such a rate that after 30 to 60 seconds it was 

 again normal. If any other part of the spectrum was 

 flashed on an amoeba which had become active in the blue 

 there was no apparent reaction, but when such a specimen 

 was exposed to direct sunlight it was clearly seen, in some 

 instances, that the streaming ceased again. 



The results obtained in these experiments lend support 

 to the general conclusions of Harrington and Leaming. 

 They differ from their results only in a few details. I 

 found red and yellow to have a slight effect on the move- 

 ment of Amoeba. Harrington and Leaming did not, prob- 

 ably owing to deficiency in light intensity or to exposure 

 in too great an intensity preceding the exposure to red or 

 yellow. I found only a very slight stimulation in the 

 violet, whereas they recorded no difference between the 

 effect of blue and violet. 



It may then be definitely concluded that the blue rays, 

 430 to 490"", have a very marked effect on the rate of 

 movement of Amoeba, while the violet, green, yellow, 

 orange and red rays have only a slight effect; and since 

 the direction of movement is in all probability regulated 

 by changes in the rate, it is evident that the blue rays are 

 also of primary importance in this process. 



