REACTIONS OF AMEBA TO LIGHT. 65 



The experiment shows that yellow light was the cause of the 

 negative behavior when both it and globulin were presented 

 together; or perhaps one ought to say yellow light, in combina- 

 tion, possessed deterring qualities which were absent when it 

 stimulated the ameba alone. Here again we have another case 

 of where the milder of two positively stimulating objects when 

 encountered alone becomes negative when encountered simul- 

 taneously with the more strongly stimulating object (Schaeffer, 



A dark spot with a piece of carbon lying in it was then placed 

 in the path of a proteus 463. As the ameba moved forward it 

 turned slightly to the left at first 467 but the tip of the ameba 

 then turned to the right and moved directly toward the dark 

 beam and carbon 471 until within about ten microns of the 

 beam, when the ameba suddenly turned to the right 472. The 

 ameba moved along in this direction without coming into contact 

 with either the dark spot or the carbon. That this decided 

 negative reaction was caused by the dark spot is evidenced by 

 the next experiment in which the carbon was omitted 481. 

 The ameba moved forward toward the dark beam for a short 

 distance, then became very uncertain in its behavior. First 

 it turned to the right, then formed a pseudopod on the left 

 through which it moved forward with the dark spot on the 

 right 484. A pseudopod was thrown out on the left but it was 

 promptly retracted 487. At the same time the tip of the pseu- 

 dopod turned very sharply to the right and moved directly 

 toward the dark spot 488. The ameba continued moving 

 toward the dark spot until within thirty microns of it 489 

 when the main pseudopod was retracted and the ameba then 

 moved away to the left through another pseudopod which had 

 been slowly forming while the ameba was moving toward the 

 dark beam. A dark beam with a piece of globulin lying in its 

 centre was placed to the right of the ameba with a pseudopod 

 already turned toward the dark spot 492. The ameba flowed 

 on through the pseudopod directly toward the dark spot. When 

 within about eighty microns of it, the tip of the main pseudopod 

 forked 495 indicating a tendency to negative behavior. The 

 left prong which became the main pseudopod, moved directly 



