222 A. A. SCHAEFFER 



turned toward the open end of the tube and a small pseudopod 

 was also sent out toward the tube — 38. The ameba, however, 

 moved away from the tube of albumin through a pseudopod 

 sent out on the right. This experiment demonstrates very 

 clearly that, although the mere presence of a solid object im- 

 mersed in a solution of some other substance serves to attract 

 an ameba, the main factor in determining the movements of an 

 ameba is either the increasing density of the diffusing molecules 

 or ions as the source of diffusion is approached, or some other 

 physical disturbance propagated radially from the source of 

 diffusion. 



(Figures 41-50 represent a control experiment showing that 

 silicic acid by itself does not cause a positive reaction.) 



Globulin and soluble egg albumin. — In an experiment similar 

 to the preceding, on the same ameba, but in which a grain of 

 globulin was used instead of silicic acid — 51, the ameba moved 

 away from the tube of egg albumin after the globulin was eaten — 

 65. This experiment, when studied in connection with the 

 preceding experiments upon this ameba, shows very strikingly 

 the nice discriminations in the selection of food which this 

 animal is capable of making. 



Carbon and lecithin. — The lecithin bore Merck's label and was 

 made from eggs. A small amount of it was smeared on a carbon 

 grain which was then laid in the path of an A. proteus — 101. The 

 ameba moved forward into contact with it, and then moved 

 off through a pseudopod which had been forming on the left — 

 107. The carbon-lecithin was then shifted — 109. The ameba 

 moved toward the test object, then turned toward the left, then 

 moved forward into contact with it again, and then moved on 

 leaving the carbon-lecithin behind. A new piece of carbon, 

 with fresh lecithin was then placed near the ameba — 115. The 

 ameba moved forward into contact with it and then passed on. 

 A small pseudopod was thrown out posterior to the carbon- 

 lecithin, and later another anterior to it, but the ameba finally 

 moved away without attempting ingestion. 



Globulin and lecithin. — A grain of globulin was smeared with 

 lecithin and placed in the same ameba's path — 123. The ameba 

 moved forward a short distance toward the test objects, then 

 turned to the left, avoiding them. 



Globulin and hematin. — A grain of hematin and a grain of 



