REACTIONS OF AMEBA TO LIGHT. 51 



the screen was about two cm. long. By means of the pinhole 

 therefore only about one fortieth of its length was projected at 

 any one time. The apparatus was rather crude and somewhat 

 unsatisfactory, but it seemed to be sufficiently reliable for ex- 

 ploratory work. 



On account of the impracticability of testing spectroscopically 

 the beams of light which were thrown into the microscope, no 

 accurate values in wave lengths can be given for blue, red, yellow, 

 etc., so there may have been, for example, a few "rays" of orange 

 or green in the yellow when that color is specified ; but such mix- 

 tures cannot have been very significant since the size of the pencil 

 of light was very small, roughly one fortieth of the length of the 

 visible spectrum. As a matter of fact some rays of all wave- 

 lengths were mixed with the pencil of monochromatic light, but 

 this defect could not be remedied, for some diffuse light (though 

 this of course might be monochromatic spectral light) is necessary 

 in order to see what is going on. But if any change in behavior 

 takes place with reference to a pencil of monochromatic spectral 

 light, the change must be caused by the more intense monocho- 

 matic light, since the diffused white light is equally intense all 

 over the field. 



A small beam of red spectral light was projected in the path of a 

 proteus 37. The ameba moved forward a short distance, then 

 sent out a pseudopod on the left 40. From this pseudopod 

 another was sent out on the right 45 which moved directly 

 toward and over the red beam. The pseudopod was soon with- 

 drawn and the ameba then moved on. 



Another proteus was brought into view with the light on the 

 right 49. The ameba turned sharply to the right, then to the 

 left, and finally moved over the red light. Presently a pseudo- 

 pod was thrown out on the right through which the ameba moved 

 away. 



In the next experiment the light was placed on the left of a 

 proteus 53. The ameba moved forward for a short distance, 

 then threw out a pseudopod on the left 56 through which the 

 ameba moved off without coming into contact with the light. 

 The ameba was then shifted with the red beam lying on the left 

 -59. As the ameba flowed forward toward the light spot a 



