436 



GENERAL BIOLOGY 



this chapter. Behavior is our only clue. By behavior we 

 judge whether a thing is alive or not. Responses alone can 

 show us whether there is anything within an organism 

 capable of taking cognizance of external conditions. And 

 responses show, also, which of the conditions of the external 

 world an organism perceives. Psychic phenomena are 

 essentially subjective, and our knowledge of them consists 

 (except in ourselves alone) in inferences based on their 

 corresponding objective manifestations. The primary rela- 

 tions existing between the subjective and the objective, may 

 be graphically stated thus : 



Objective 

 phenomena 



Stimulus 



Subjective 

 phenomena 



Sensation 



Act ^JgJ! Impulse 



This is merely a graphic statement of the evident facts 

 that environment (external or internal) gives the stimulus, 

 which upon the psychic side, produces the sensation (feeling, 

 taste, sight, etc.), which may be accompanied by an impulse 

 (also subjective), and may eventuate in an act. The act, 

 therefore, is thus the last link in a chain of events: the effect 

 of a succession of causes. However diverse the structure of 

 organisms, their parts that are most directly subservient to 

 the psychic life are of two sorts : 



1) Receptive organs, capable of being influenced by 

 stimuli. These are the parts through which the external 

 world makes its impressions upon the sensory mechanism. 



2) Active or motor organs, capable of making appropriate 

 responses. These are the parts through the agency of which 

 the psychic states are made manifest. 



