MENTAL EVOLUTION OF MAN 239 



stream, but we do know that salts and water and other 

 dead substances may enter into the composition of the 

 material brain which is the physical basis of mind. 



In my opinion the individual argument renders the 

 monistic conception of mind and matter unassailable. 

 The food that we may eat and the water we may drink 

 are dead, and as such they display absolutely no evi- 

 dence of nervous or mental processes. When they 

 enter our bodies, they with other foods replenish the 

 various tissues, and among these the parts of the brain. 

 In a material sense they become actual living proto- 

 plasm, replacing the worn-out substances destroyed 

 during our previous thinking ; and their properties are 

 combined to make brain and thought, to play for a 

 time their part in life, and to pass back into the world 

 of dead, unthinking things. Every one of us knows 

 that hunger reduces our ability to think clearly and 

 fully, and every one knows also that mental vigor is 

 renewed when fresh supplies of nourishment reach the 

 brain. What can be the source of mentality, if it is 

 not something brought in from the outer world along 

 with the chemical substances which taken singly are 

 devoid of mind? Scientific monism frankly replies 

 that it is unable to find another origin. 



We are thus brought to recognize, not only the 

 continuity taught by organic evolution, but also the 

 uniformity of the materials constituting the entire 

 sensible world, inasmuch as the ultimate unit of all 

 nervous phenomena is the reflex act of a protoplasmic 

 mass, which itself is a synthesis of properties inhering 

 in the chemical elements making up living matter. 

 Among inorganic things the mind-stuff units are com- 



