OF MICRO-ORGANISMS. 3 



ment. It is customary to apply to the union of these 

 two properties the name irritability, which expresses 

 the reaction of the micro-organism upon exterior 

 forces. It is therefore held, and with reason, that 

 every living cell is irritable, that is to say that it pos- 

 sesses the property of responding by movements to 

 the excitations which it suffers. 



In admitting then that irritability is the founda- 

 tion of the life of relation, and consequently also the 

 foundation of psychology, we must nevertheless guard 

 against comparing the autonomous cell of micro- 

 organisms to a simple irritable cell. Although the 

 body of these small beings may be equivalent to a 

 simple cell, it would be an error to believe that their 

 life of relation consists in a motory reaction consequent 

 upon exterior irritation. At the close of our investiga- 

 tions into the psychology of Proto-organisms we shall 

 see that, in these inferior beings which represent the 

 simplest forms of life, we find manifestations of an in- 

 telligence which greatly transcends the phenomena of 

 cellular irritability. Thus, even on the very lowest 

 rounds of the ladder of life, psychic manifestations are 

 very much more complex than is usually believed, and 

 the conception of cellular psychology which some very 

 recent authors have formed, seems to me a very crude 

 analysis of the most delicate of phenomena. 



In the great majority of pluricellular animals, the 

 life of relation is exhibited in a nervous system and 

 in a muscular system. In Micro-organisms the same 

 cannot be said to be the case: the greater part possess 

 neither a central nervous system nor organs of sense; 

 some even lack organs of locomotion. The functions 

 of the life of relation are performed by the entire 

 mass of the body: many of the Protista, for example, 



