228 A. A. SCHAEFFER 



plasmic current was changed four times. The sides of the 

 ameba were then stimulated at various places with the alga 

 threads and at each point a pseudopod was thrown out. If 

 the stimulating was done properly, food cups were begun at 

 these pseudopods. Partial or complete food cups could be 

 formed at will, depending upon the character and continuance 

 of the stimulus. In short, all the ordinary items of positive 

 reacting, from simple movement toward a stimulus to the prompt 

 and complete formation of a typical food cup, could be produced 

 by varying the intensity, frequency, and character of the stim- 

 ulus. The mechanical stimuli proceeding from the alga threads 

 were probably the only ones concerned in producing the reac- 

 tions described, for the bottom of the dish was strewn with 

 broken oscillatoria filaments, over which the ameba frequently 

 flowed without changing its behavior. It was only when the 

 filaments were agitated in contact with the ameba, or nearly in 

 contact with it, that the ameba responded with a positive reac- 

 tion. The efficiency of this sort of stimulation lies doubtless in 

 the fact that the great flexibility of the alga threads permits 

 one to simulate to a high degree the movements of small living 

 organisms. 



An experiment similar to this one gave almost identical results. 

 A large binucleate A. proteus that had reacted indifferently to 

 globulin grains or eaten them imperfectly was stimulated with 

 the alga threads and the response was the formation of a com- 

 plete food cup — FCi, 220. The ameba was stimulated again 

 and another food cup was started, FC 2 . A grain of globulin 

 was then dropped into the partly formed food cup and upon 

 further stimulation the food cup closed completely. The glob- 

 ulin was retained for over two hours, when observation was 

 terminated. The first food cup which was formed, it is inter- 

 esting to note, remained almost undiminished in size for over 

 two hours. It remained much longer than if it had contained 

 food. 



In another experiment of a similar nature the glass needle 

 was used without any alga threads or anything else on it — 194. 

 The point of the needle was agitated near, but not in contact 

 with, an A. proteus. A pseudopod was promptly started in 

 the stimulated region — 195, and it attained to considerable size 

 and finally formed itself into a food cup, which was, however, 



