The Animal Mind 



side stimulated in the case of the electric current, the side 

 toward the positive pole contracts as a whole, and the 

 movement takes place in the opposite direction. These phe- 

 nomena constitute the negative reaction (Fig. i). 



Secondly, the reaction to solid bodies sometimes takes a 

 positive form. In this case a pseudopodium is pushed for- 

 ward in the direction of the stimulus, and the animal moves 



toward the solid. As the nega- 

 tive reaction serves the purpose 

 of avoiding obstacles, so the 

 positive reaction is useful in 

 securing contact with a support 

 on which to creep, and with 

 food. It seems to be given in 

 response to weak mechanical 

 stimuli, stronger ones producing 

 the negative reaction. No 

 chemicals have been found to 

 occasion it, but weak chemical 

 stimulation very likely cooper- 

 ates with mechanical stimula- 

 tion when the positive reaction 

 is given to food. 

 Thirdly, there is the food-taking reaction. This consists, 

 for Amceba proteus, in the pushing forward of a pseudopodium 

 on either side of the particle of food that has come into con- 

 tact with the animal ; the bending over of the ends of the pseu- 

 dopodia so as to grasp the food, while "a thin sheet of pro- 

 toplasm" spreads from the upper surface of the animal over 

 it ; and the final fusion of the ends of the pseudopodia and the 

 ends of this sheet, so as to take the food directly into the ani- 

 mal's body. The reaction may occur anywhere on the body 

 surface, there being no specialized mouth. It appears to be 



FIG. i. Negative reaction of 

 Amoeba to stimulation by a glass 

 rod. a. Application of the stim- 

 ulus, b. Change of direction 

 of movement. After Jennings 



(211). 



