20 BEHAVIOR OF THE LOWER ORGANISMS 



rent this is not so evident at first view. The Amoeba reacts even though 

 the light or current remains constant. But if, as appears to be true, the 

 stimulation occurs primarily on that side on which the light shines, or on 

 the anode side in the reaction to electricity, then it is true that even in 

 these cases the reacting protoplasm is subjected to changes of conditions. 

 Since the movement of the Amoeba is of a rolling character, the proto- 

 plasm of the anterior end and that of the posterior end continually in- 

 terchange positions. In an Amoeba moving toward the cathode the 

 extended protoplasm at the cathode end is gradually transferred to the 

 anode end, and as this change takes place it contracts. In the reaction 

 to light the protoplasm of the anterior end directed away from the light 

 is gradually transferred in the rolling movement to the lighted side ; it 

 then contracts. It is therefore possible that in these cases also it is the 

 change from one condition to another that causes reaction. 



It is notable that changes from one condition to another often cause 

 reaction when neither the first condition nor the second would, if acting 

 continuously, produce any such effect. Thus, Amoebae react negatively 

 to tap water or to water from a foreign culture, but after transference to 

 such water they behave normally. Harrington and Learning (1900) 

 show that when white light is thrown on an Amoeba it ceases to move, 

 but if this light continues, the animal resumes movement. To constant 

 conditions Amoeba tends to become acclimatized. 



But even constant conditions may induce reaction if they interfere 

 seriously with the life activities of the animal. Under great heat or 

 strong chemicals the protoplasm contracts irregularly and remains thus 

 contracted till death follows. A different example of the production of 

 a reaction by constant conditions is shown in the behavior of Amoebae 

 suspended in the water. Under these conditions, as we have seen, the 

 animal sends pseudopodia in all directions, taking a starlike form. It 

 is evident that the general condition of the organism, as well as an 

 external change, may determine a reaction. 



The fact that the nature of the behavior depends on the general con- 

 dition of the organism is illustrated in another way by the observation 

 of Rhumbler, that Amoebas may begin to take food, then suddenly reject 

 it. This rejection occurs especially after subjection to light. Appar- 

 ently the Ught changes the condition of the animal in such a way that it 

 no longer reacts to food as it did. 



In Amoeba, as in higher animals, the localization of the stimulation 

 partially determines the reaction. The result of stimulation on the 

 right side is to cause movement in a direction different from that pro- 

 duced by stimulation on the left side. In Amoeba the relation of the 

 movement to the localization of the stimulus is very simply determined. 



