REACTION IX AMOEBA TO LIGHT 
273 
strong red light but soon began again. If they were now exposed 
to green the movement again ceased; the same was true for blue 
after green and for direct sunhght after blue. A change from direct 
sunlight to blue, blue to green, or green to red, produced no appar- 
ent effect. After being exposed to any color or any combination 
of colors for a short time the movement was resumed. In direct 
sunlight or in blue light it required longer than in green or red. 
As a matter of fact in these two colors, in the red in particular, 
there was no cessation of movement in some specimens, and only 
a shght decrease in others, while in still others the movement 
stopped entirely. In case of direct sunlight or blue, on the other 
hand, the movement stopped abruptly in nearly every specimen 
almost as soon as exposed. Similar but somewhat more detailed 
results were obtained in the spectrum. 
In making the observations in the spectrum 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 amoe- 
bae 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 prism 
was 2 mm. wide and the spectrum on the slide nearly 3 cm. 
long. There was consequently some overlapping 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 which was active in 
this light had been selected, it was suddenly exposed to any de- 
sired part of the spectrum and the reaction noted. 
Many observations were made on numerous individuals between 
10 A.M. and 1 P.M. June 16 and 18. The sky was clear and the 
intensity of light consequently at a maximum, approximately 
5000 candle meters. Without going into details with reference 
to reactions of individual specimens it may be stated that the effect 
of sudden exposure to red, yellow or violet after very faint diffuse 
