600 RAYMOND PEARL. 



c. The General Features of the Reactions to 

 Mechanical Stimuli. — From the above description it 

 appears that the nature of the reactions to mechanical stimuli 

 depends upon several factors. These are — 



1. The intensity of the stimulus. 



2. The localisation of the stimulus. 



3. The physiological condition of the organism. 



The reactions given may be of several different kinds, de- 

 pending on the factors mentioned above. These are chiefly 

 as follows : 



1. The resting individual may begin locomotion. 



2. The gliding movement may be changed to the crawling 

 movement. 



3. The forward movement may be transformed to move- 

 ment backward. 



4. The animal may turn away from the source of the 

 stimulus (the "negative " reaction). 



5. The animal may turn towards the source of the 

 stimulus (the "positive " reaction). 



It is evident that the reactions last named — the negative 

 and positive reactions — are the most important and most 

 interesting from the theoretical standpoint. It is of the 

 greatest interest to note that these two qualitatively opposite 

 reactions are induced merely by differing intensities of 

 stiumli, the stimuli being otherwise identical throughout. 



It is to be noted further that the positive and negative 

 reactions have the characteristics of purely reflex acts. Each 

 reaction has a perfectly definite and characteristic form. 

 While, in some cases, which of the two reactions will be 

 given in response to a particular stimulus depends on the 

 physiological condition ot" the organism, yet it is practically 

 always either one or the other of the typical reactions. Only 

 very rarely do we get any deviation from the type forms, 

 and in such cases the reaction is evidently a combination of 

 easily recognisable components of the two typical complexes 

 of reflexes. 



These two reactions are evidently not single simple 



