MEMORY IMAGES 171 



show the addition necessary to the tropism theory to make 

 it include the endless number of reactions in which associa- 

 tive memory is involved. The psychiatrist would find it 

 easy to supply numerous examples of this type of forced 

 movements toward certain objects which have left a 

 memory image. Since the writer has not investigated 

 this subject sufficiently he is not in a position to give more 

 than a suggestion for the direction of further work. He 

 is inclined to believe that with this enlargement the trop- 

 ism theory might include human conduct also if we realize 

 that certain memory images may exercise as definite an 

 orienting influence as, e.g., moving retina images or sex 

 hormones. 



This tentative extension of the forced movement or 

 tropism theory of animal conduct may explain why higher 

 animals and human beings seem to possess freedom of 

 will, although all movements are of the nature of forced 

 movements. The tropistic effects of memory images and 

 the modification and inhibition of tropisms by memory 

 images make the number of possible reactions so great 

 that prediction becomes almost impossible and it is this 

 impossibility chiefly which gives rise to the doctrine of 

 free will. The theory of free will originated and is held 

 not among physicists but among verbalists. We have 

 shown that an organism goes where its legs carry it and 

 that the direction of the motion is forced upon the organ- 

 ism. When the orienting force is obvious to us, the motion 

 appears as being willed or instinctive ; the latter generally 

 when all individuals act alike, machine fashion, the former 

 when different individuals act differently. When a swarm 

 of Daphnia is sensitized with C0 2 they all rush to the 

 source of light. This is a machine-like action, and many 



