Nos. 622-623] MIGRATION A FACTOR IN EVOLUTION 475 



terns, as expressed by Bancroft, there are those which 

 reinforce or accelerate (tend to continue or hasten activ- 

 ity) and do not change its character, but only the inten- 

 sity of the response (temperature, enzymes, repetition, 

 etc.). By this method also systems tend to be perpetu- 

 ated, and organisms in " favorable ' ' (non-interfering) 

 conditions, tend to continue their normal activities.' 

 This law appears to be a corollary of Bancroft's law 

 which is concerned with interference or retardation. 

 Thus when a system is reinforced, rather than disturbed, 

 the system continues onward in its normal cycle without 

 interference, and may even be accelerated in its act ivities. 

 This is a condition which may maintain a relative equi- 

 librium, or increase stress. The intensity of interference, 

 or reinforcement, and its repetition, hastens or retards 

 the rate of change of a system. We thus have the quali- 

 tative and quantitative relations applying to the law of 

 reinforcement or acceleration of the equilibrium, and 

 Bancroft's law of interference with its development. 



Even relatively fixed and automatic responses of be- 

 havior may be looked upon much as the relatively stable 

 structural characters, so that every sort of behavior, even 

 to the process of higher learning, shows this regulatory 

 influence which tends to change in such a manner as to 

 eliminate all disturbance with its systems, even to the in- 

 consistencies of our ideals. 



Thorndike ('11, p. 244) in summarizing the laws of 

 "acquired behavior or learning" formulates two laws. 

 The first is essentially a statement of Bancroft's law of 

 response to interference (discomfort or satisfaction), 

 and the second (exercise or repetition), is that of rein- 

 forcement. This means that the kind and intensity of 

 stimulation, and its repetition are the laws of establish- 

 ing associations, or of changing the system, and that in- 

 tensity and repetition act as the catalyzers which influ- 

 ence the speed of modification of the system ; at bottom it 

 therefore appears we have qualitative and a quantitative 



