47^ H. S. Jennings. 



purpose or idea in the mind of the organism, or any "psychoid" 

 or entelechy to account for the change of behavior, for an adequate 

 objective cause exists. We know experimentally that the dark- 

 ness or the lack of oxygen interferes with the metabolic processes. 

 This very interference is then evidently the cause of the change 

 of behavior. When anything interferes with the internal pro- 

 cesses, running with much energy, the energy overflows in other 

 directions, resulting in changes in behavior. This statement is a 

 mere generalized formulation of the facts determined by observa- 

 tion and experiment in the most diverse organisms. 



Internal as well as external interference may cause the changes 

 of behavior. If oxygen or other material for metabolism is 

 lacking to such an extent as to interfere with the metabolic pro- 

 cesses, the organism changes its behavior. In the sea anemones, 

 as we have seen in the preceding paper, this condition induces the 

 animal to change its position and start off on a laborious tour of 

 exploration. The initiation of changes in movement through 

 internal conditions gives the basis for the reactions which we call 

 positive, as we shall see. 



The answer to our first question is then as follows: The 

 organism changes its behavior as a result of interference with its 

 physiological processes. 



Our second question was: How does it happen that such 

 movements are produced as bring about more favorable con- 

 ditions.'' This question we have already answered, so far as 

 many lower organisms are concerned, in our general statement 

 on page 474. The organism does not go straight for a final end. 

 It merely acts — in all sorts of ways possible to it — resulting in 

 repeated changes in the conditions. In this way a condition is 

 after a time reached that relieves the interference with the internal 

 processes. 



The nature of the changes in behavior produced — the move- 

 ments that occur in any given organism — depend on what may 

 be called the "action system" of the organism. The animal, in 

 other words, performs the movements that it is accustomed to 

 perform, as determined by its structure and its past history. 

 The essential fact is that interference with the internal processes 

 causes a change in behavior. The mere fact of a change under 

 these conditions tends in itself to be regulatory. The original 

 behavior has brought on the interfering conditions, hence the 



