190 THE BEHAVIOR OF LOWER ORGANISMS. 



As a control experiment, distilled water was used in the tube in 

 place of a chemical in solution. Amoeba was found to react negatively 

 to this also, though the reaction was less marked than with most of the 

 chemicals. But this result, of course, rendered the experiments with 

 solutions of chemicals in the tube indecisive, as the Amoeba may have 

 reacted to the distilled water in which the 11 solutions were made up. 

 The solutions were, therefore, made up with culture water, and the 

 same results were obtained as before. 



The results with the chemicals show merely that Amoeba responds 

 negatively to almost any solution differing markedly from that in which 

 the animal is immersed, the precise chemical composition of the solu- 

 tion being of little consequence. The animal responded negatively not 

 only to distilled water and to the chemicals mentioned, but also to tap 

 water, and to water taken from other cultures than that in which the 

 specimens occurred. 



REACTIONS TO HEAT. 



Verworn (1889, pp. 64-67) studied the directive influence of heat on 

 the locomotion of Amoeba by concentrating the sunlight on a small por- 

 tion of the slide and leaving the rest dark, then observing the behavior 

 of the Amoeba on coming to the boundary of this lighted and heated area. 

 The effects of the light proper were excluded by control experiments. 

 It was found that on coming to the heated area Amoeba remained quiet 

 a moment, then contracted on the heated side, and sent out a pseudopo- 

 dium on the opposite side. It then crept away in the direction indicated 

 by this pseudopodiutn (" negative thermotropism"). 



My experiments differed from those of Verworn in employing con- 

 ducted heat in place of radiant heat ; thus there was no possibility of 

 a complication from the effects of light. As Verworn sets forth, it is 

 difficult to warm only one side of so small an object as an Amoeba. I 

 succeeded x however, in doing this in a very sinfple manner. For each 

 experiment an Amoeba was selected that was creeping on the under 

 surface of the cover glass. This was placed in focus under an objective 

 of a considerable focal distance, yet of high enough power so that the 

 internal movements could be seen. A needle was then heated in a flame 

 and its point was brought against the cover glass a short distance in 

 advance of the Amoeba. Control experiments had shown that the use 

 of a needle at room temperature had no effect. 



If the heated needle was placed at a proper distance from the Amoeba, 

 the phenomena follow as described by Verworn (/. c.}. There was a 

 short pause, then the side next to the needle contracted. A current 

 of protoplasm passed toward the opposite side, at times meeting the 

 current already in existence. A new pseudopodium was sent out, either 

 on the side opposite the needle, or, in many cases, in a direction inter- 



