330 LIGHT AND THE BEHAVIOR OF ORGANISMS 



ments a horizontal beam of direct sunlight was passed 

 through a vertical prism and thrown on the mirror below 

 the stage of the microscope, from which it was reflected 

 to the slide. By manipulating the mirror the amoebae on 

 the slide could be suddenly subjected to light in any part 

 of the spectrum, and the color to which they were exposed 

 could be instantaneously changed. 



The vertical slit in the opaque screen over the face of 

 the lens was 2 mm. wide and the spectrum on the slide 

 nearly 3 cm. long. There was consequently some over- 

 lapping of rays in adjacent parts of the spectrum, but there 

 was no intermingling of rays in distant parts. For example, 

 in the red there was some orange, but no rays of shorter 

 wave lengths. 



The amoebae were examined in daylight so faint that 

 they could scarcely be seen. After a specimen active in 

 this light had been selected, it was suddenly exposed to 

 any desired part of the spectrum and the reaction noted. 



Many observations were made on numerous individuals 

 between 10 a.m. and i p.m., June 16 and 18. The sky 

 was clear, and the intensity of light consequently at a 

 maximum, approximately 5000 ca. m. Without going into 

 details with reference to reactions of individual specimens 

 it may be stated that the effect of sudden exposure td 

 red,^ yellow or violet after very faint diffuse sunlight was 

 essentially the same. There was in many specimens a 

 slight decrease in rate of movement, in some a momentary 

 cessation, and in others no apparent reaction whatever. 

 In the green the effect was similar to that in red, yellow 

 and violet, only somewhat more marked. To obtain the 



* The wave lengths are designated in terms of color. 



Red = 630-760'^'' 



Orange = 590-630^^ 



Yellow = 560-590'^'' 



Green — 490-560'^'' 



Blue = 430-490'^'' 



Violet = 395-430'''' 



Ultra-violet = 340-395''^ 



