OF MICRO-ORGANISMS 109 



vres attending conjugation. This act of selection is a 

 capital phenomenon; we may take it as the character 

 istic feature of functions pertaining to the nervous 

 system. As Romanes has indeed observed, the power 

 of choice may be regarded as the criterion of psy- 

 chical faculties. Going farther, we might be able to 

 say that selection comprehends the properties of the 

 nervous cellule, as irritability comprehends the prop- 

 erties of the muscular cellule. 



Scientists have endeavored to explain the mechan- 

 ism of this choice. They have pretended to solve it 

 by saying that it was dependent upon the relation be- 

 tween the chemical composition of the cellule making 

 the choice and the chemical composition of the bod)' 

 selected. 



Such explanations are purely verbal. Undoubt- 

 edly, the faculty of selection, of which protoplasm 

 seems to be possessed, is founded in the character 

 of its chemical composition. Chemistry lies at the 

 basis of physiology, but chemistry does not explain 

 physiology, and it is quite evident that that property 

 which protoplasm possesses of making a choice be- 

 tween several excitations, is a physiological property. 



However that may be, we may resume all the fore- 

 going into the statement that every micro-organism 

 has a psychic life, the complexity of which transcends 

 the limits of cellular irritability, from the fact that 

 every micro-organism possesses a faculty of selection; 

 it chooses its food, as it likewise chooses the animal 

 with which it copulates. 



M. Richet has defended his opinion in opposition 

 to the one I have propounded, in a note published in 

 the Revue Philosophique for Febuary 1888, wherein he 

 speaks as follows: 



