THE MOVEMENTS AND REACTIONS OF AMCEBA. 191 



mediate between this and the original one. The phenomena are in all 

 respects identical with those seen in the negative reaction to mechanical 

 stimuli. If the needle is brought a little nearer, so that the heat acts 

 more strongly, there is a sudden strong contraction of the side affected. 



Simultaneously with this there is often, as in the case of strong 

 mechanical stimuli, a sudden rush of the internal fluid toward the side 

 stimulated. This lasts but an instant and is succeeded by a current 

 away from the stimulated side, the formation of a pseudopodium on the 

 unstimulated side, and locomotion in that direction. The sudden rush 

 of internal contents toward the side affected is, I think, clearly due to 

 the cause suggested under mechanical stimuli. Part of the posterior 

 portion of the attached area of the Amoeba is loosened from the substra- 

 tum by the sudden contraction at the front end ; this portion, therefore, 

 contracts quickly and sends a current forward, as described on p. 168. 



When the heat is still more powerful the entire Amoeba is affected. 

 It contracts and at the same time loses its attachment to the substratum. 

 There is a strong momentary rush of the internal fluid toward the end 

 which had been anterior, due to the cause set forth in the preceding 

 paragraph. This ceases and the body becomes very irregular and ceases 

 to move. 



The reaction to local stimulation by heat is thus of essentially the 

 same character as the reaction to mechanical stimuli and to chemicals. 



Like Verworn (1889, P- ^7), I have been unable to obtain a reaction 

 to cold in Amoeba. 



REACTIONS TO OTHER SIMPLE STIMULI. 



The reactions of Amoeba to electricity and to light have been thor- 

 oughly studied by other authors, so that it will not be necessary to treat 

 them in detail here. Only certain especially important points will be 

 touched upon. 



The reactions of Amoeba to the continuous electric current have 

 been studied in detail by Verworn (1890, a; 1897). I have repeated the 

 experiments in order to determine by observation the direction of the 

 surface currents of protoplasm during the reaction. For this purpose 

 soot was mingled with the water containing the Amoebae, and the elec- 

 tric current was passed through the preparation. The typical reac- 

 tion as described by Verworn was observed in many cases, but the 

 surface currents, of course, cannot be seen unless soot is resting upon or 

 is attached to the surface of the animal, which happens only rarely. 

 Finally a specimen of Amoeba proteus was observed with a string of 

 soot particles attached to one side (Fig. 72). The electric current was 

 then passed through the preparation in such a way that the side bearing 

 the soot was next to the anode (Fig. 72, a). The Amoeba thereupon 



