Modifiability in Behavior. 47 1 



of conduction, but is the relation of the action of the external agent 

 to the internal processes. The problem presented by the fact that 

 the same stimulus, in the same intensity, applied to the same part 

 of the body, produces qualitatively different and even opposite 

 results, depending on the inner metabolic states, seems not to have 

 received the attention it deserves. It evidently places marked 

 difficulties in the way of a simple mechanical conception of the 

 reflex process, based merely on the anatomical structure of the 

 organism. The internal physiological state determines in some 

 way which of various courses within the body the transmitted 

 stimulus shall follow and what organs it shall arouse to activity. 

 The organism cannot be looked upon as a static structure, on 

 which external agents must act in a simple invariable way. The 

 organism is a process, and some of the chief determining factors in 

 behavior are given by the relation of the internal to the external 

 processes. As the internal processes change, the reaction to 

 external agents changes correspondingly. We find that reactions 

 which assist the existing internal processes are continued or 

 repeated, while those which oppose them are changed. This 

 gives one of the chief bases for the regulatory character of behavior, 

 as I shall attempt to set forth in farther detail in the paper which 

 follows the present one. The metabolic processes, while the most 

 striking of those taking place in the lower organisms, are of course 

 not the only ones occurring in animals. An immense number of 

 other processes are in progress, and the relation of external agents 

 to these processes may and does equally determine behavior. 

 This gives the phenomena of behavior their complexity, prevent- 

 ing them from being in relations of simple dependence on external 

 agents, as they are often represented of late. Such a view quite 

 underestimates the difficulty of the problem of behavior. The 

 dependence on external agents exists, but is complex, and can 

 usually not be predicted without a knowledge of the present 

 internal state of the organism — this depending on its past history 

 and the course of its various internal processes. 



It would of course be more convenient if the problems of 

 behavior were as simple as they are often proclaimed to be. 

 Work revealing their complexity is naturally not received with 

 the acclaim that greets the announcement that all these things 

 are simple and easy. But if our object is really to obtain control 

 of the vital processes, then we must face them in all their com- 



