The Mind of the Simplest Animals 43 



more complex and variable than Jennings's account de- 

 scribes it to be. They observed cases where only one 

 pseudopodium was formed, and cases where it was put forth 

 not at the exact point acted upon by the stimulus. The 

 nature of the reaction varied in such a way as to prevent 

 the "swallowing" of too much water along with the food: 

 "the parts that could most advantageously respond did 

 so." McClendon (451 a) has attempted to apply the surface 

 tension theory to the positive, negative, and feeding re- 

 actions of Amoeba, suggesting that the stimuli may exert 

 an electric influence whereby the surface tension at the point 

 stimulated becomes less in the case of the positive reactions 

 and feeding, greater in the negative reaction. But such 

 variations as those just described are difficult to reconcile 

 with a surface tension theory. Moreover Mast and Root 

 (477) have observed Amoeba crushing its prey with a 

 force far greater than surface tension could account for. 

 Schaeffer (658) suggests that a chemical discrimination may 

 occur inside the Amoeba after substances have been taken 

 in, for, he says, when carmine grains have been swallowed, 

 the Amoeba at once begins to move off in such a way as to 

 bring the grains to the hinder part of the body where they 

 will be ejected. "The carmine grains areiejected . . . be- 

 cause they are actually disagreeable and not merely because 

 they are (presumably) indigestible." A hungry Amoeba, 

 when it comes within 100 thousandths of an inch from an 

 organism, which is as a whole at rest but moving certain 

 portions of its body, will begin to move towards it and to 

 form a food cup before actual contact occurs. Probably 

 the slight water currents produced by the movements of 

 the prey act as the stimulus in this case. Any stimulus 

 which proceeds from a moving object tends, as we shall 

 see, to be peculiarly effective. 



