REACTIONS OF AMEBA TO LIGHT. 53 



the light. When it came into contact with the light it forked, 

 the limbs moving forward with the light spot between them 

 -133. The right limb became the main pseudopod through 

 which the ameba moved off. 



A beam of red light was projected to the right of another 

 proteus 167. The tip of the ameba turned slightly toward the 

 left, then resumed its original direction. The ameba was then 

 shifted with the red light on the left 170. There was at first a 

 tendency for pseudopods to form on the right, but, as the ameba 

 moved forward, two were formed on the left in the region of the 

 light. One of them moved a considerable distance toward the 

 light 174 but was then retracted as a pseudopod on the right 

 was thrown out to become eventually the main pseudopod. The 

 ameba was then shifted with the red light lying on the left 176. 

 As the ameba moved forward a large pseudopod was thrown out 

 on the left, directly toward the light. This pseudopod became 

 the main one through which the ameba moved away. 



Summary. Red spectral light produces about the same changes 

 in behavior as white light. The vertical beam of red light is 

 sensed at a distance, and in almost all cases produces positive 

 behavior. In some few cases an ameba may behave indifferently 

 or even negatively; but if the experiments are repeated several 

 times a positive reaction is almost sure to occur. Amebas are 

 therefore not negative or positive permanently with respect to 

 beams of red light, but the behavior may readily change from 

 the one to the other aspect. Red light of the intensity used 

 does not seem to stimulate the ameba disagreeably when it 

 moves into direct contact with the beam of light, for in a number 

 of cases the ameba moved on over the light without visible change 

 of behavior. In some respects the ameba tended to encircle the 

 source of light in the same manner in which it sometimes encircles 

 solid objects. 



Blue Light. A beam of impure 1 blue spectral light was pro- 

 jected to the right of a proteus 135. The ameba turned to the 



1 Between the grating and the arc was placed twenty cm. of distilled water con- 

 taining a very little ammoniacal copper sulphate. The copper salt gave rise to a 

 subsidiary faint yellowish spot of light not quite coinciding with the blue. The 

 yellow image disappeared when the copper salt was omitted from the distilled water. 

 The yellow image was probably due to fluorescence of the copper sulphate. 



