CHOICE OF FOOD IN AMEBA 221 



REACTIONS TO TWO PARTICLES OF DIFFERENT CONSTITUTION 



LYING CLOSE TOGETHER 



Globulin and silicic acid. 1 — A grain of globulin and a grain of 

 silicic acid were laid close together in the path of an Amoeba 

 proteus 2 — figure 1. The test objects were laid some distance 

 ahead so that all the changes in behavior due to the test sub- 

 stances could be observed. The ameba moved directly forward 

 for a considerable distance, then sent out on either side several 

 pseudopods which were, however, soon retracted — 3. As the 

 ameba moved further forward toward the test substances, it 

 broke up into three pseudopods, the middle one of which pointed 

 directly toward the silicic acid, though it did not move into 

 contact with the acid — 5. The right-hand pseudopod was 

 retracted while the ameba moved on through the pseudopod 

 on the left, gradually swinging around the silicic acid, and 

 coming into contact with the globulin from the opposite direc- 

 tion. The globulin was ingested without the formation of a 

 food cup, while the silicic acid was carried to the back of the 

 ameba where it remained a short time. 



Silicic acid and egg albumin. — The ameba whose reactions to 

 'globulin and silicic acid were described above, later reacted 

 positively to, but finally avoided, a capillary tube containing a 

 solution of egg albumin — 14. After this test a grain of silicic 

 acid was laid in front of the tube of albumin — 26. The ameba 

 moved toward the silicic acid until within about fifty microns 

 of it when there were formed several side pseudopods, of which 

 the one on the right became the main pseudopod. But this 

 one soon curved to the left and toward the silicic acid, and 

 then kept on moving in this direction until within thirty microns 

 of the acid when the tip of the main pseudopod turned slightly 

 to the right and moved past the test object — 35. But as soon 

 as the tip of the ameba was well past the silicic acid, the ameba 



1 For method of preparation of the test substances mentioned in this paper 

 reference should be made to my former papers, '16b, '16c. 



2 For a description of the species of ameba mentioned in this paper refer to my 

 paper '16d, in Science. In previous papers I spoke of 'raptorial' and 'granular' 

 amebas. Raptorial amebas are of the species Amoeba dubia Schaeffer, while the 

 granular amebas refer to two species: Amoeba proteus Pallas emend. Leidy, and 

 Amoeba discoides Schaeffer. From my notes I am unable to tell in all cases to which 

 of the latter two species the granular amebas belonged. This is due to the fact 

 that discoides was not discovered to be distinct from proteus until after these 

 experiments were made. In this paper therefore, the label A. proteus includes also 

 the species discoides. 



