58 MAN AN ADAPTIVE MECHANISM 



Action Patterns 



Somewhere in the tissues of Venus' fly-trap and of 

 other organisms having reflex arcs there exists a tend- 

 ency always to produce the same response to a given 

 stimulus, that response being achieved by means of a 

 mechanism acquired for its performance by natural se- 

 lection. This mechanism may be described as a scheme 

 or pattern of action, a pattern specific to that organism 

 and possible of excitation only by that stimulus which 

 gave rise through selection' to the mechanism itself. 

 Upon the number of his " action patterns" and the 

 responses which are elicited by their excitation depend 

 the life processes of the individual organism whether 

 man or lower animal. The exact nature of the motor 

 or action pattern we are not prepared to discuss. 

 For the present it is sufficient to state our belief that 

 every adaptive reaction corresponds to the plan of 

 the muscular reflex occurring automatically in re- 

 sponse to a primary excitation from without and 

 being accompanied by a discharge of potential energy 

 which may be measured by the depleted vitality of the 

 organism. We consider also that every adaptive 

 reaction is expressed in heat or motion in whatever 

 form is of use to the individual. 



As we have seen, the presence of the adequate stimu- 

 lus is the first requisite for reaction. As the lobes 

 of the fly-catching plant close only upon the arrival 

 of the insect stimulus, so every conceivable act, thought 

 or function of the human body requires an adequate 

 stimulus for its manifestation, that manifestation de- 

 pending absolutely upon the previous experience of 



