292 BEHAVIOR OF THE LOWER ORGANISMS 



Yerkes found that a very large number of repetitions were necessary 

 before a given resolution was established. 



I (n) Different Factors on which Behavior Depends. We have seen 

 'that the behavior of the organism at a given moment depends on its 

 physiological state, and that it therefore secondarily depends upon all 

 the factors upon which the physiological state depends. Hence we can- 

 not expect the behavior to be determined alone by the present external 

 stimulus, as is sometimes maintained, for this 'is only one factor in 

 determining the physiological state. The behavior at a given moment 

 may depend on the following factors, since these all affect the physio- 

 logical state of the organism : 



1. The present external stimulus. 



2. Former stimuli. 



3. Former reactions of the organism. 



4. Progressive internal changes (due to metabolic processes, etc.). 



5. The laws of the resolution of physiological states one into another. 

 All these factors have been strictly demonstrated by observation and 



experiment, even in unicellular organisms. Any one of these alone, 

 or any combination of these, may determine the activity at a given 

 moment. 



