THE NATURE OF THE PROBLEM. 17 



first place, and, secondly, of the inner sense-centres 

 in the cortex of the brain. The microscopic elementary- 

 organs of the former are the sense-cells ; of the latter, 

 groups of ganglionic cells. The experiences which 

 we derive from the outer world by these invaluable 

 instruments of our mental life are then moulded into 

 ideas by other parts of the brain, and these, in their 

 turn, are united in a chain of reasoning by association. 

 The construction of this chain may take place in two 

 different ways, which are, in my opinion, equally 

 valuable and indispensable : induction and deduction. 

 The higher cerebral operations, the construction of 

 complicated chains of reasoning, abstraction, the forma- 

 tion of concepts, the completion of the perceptive 

 faculty by the plastic faculty of the imagination — in 

 a word, consciousness, thought, and speculation — are 

 functions of the ganglionic cells of the cortex of the 

 brain, just like the preceding simpler mental functions. 

 We unite them all in the supreme concept of reason. 1 

 By reason only can we attain to a correct know- 

 ledge of the world and a solution of its great problems. 

 Reason is man's highest gift, the only prerogative that 

 essentially distinguishes him from the lower animals. 

 Nevertheless, it has only reached this high position by 

 the progress of culture and education, by the develop- 

 ment of knowledge. The uneducated man and the 

 savage are just as little (or just as much) " rational " 

 as our nearest relatives among the mammals (apes, 

 dogs, elephants, etc.). Yet the opinion still obtains 

 in many quarters that, besides our god-like reason, we 

 have two further (and even surer !) methods of receiving 

 knowledge — Emotion and Revelation. We must at 



1 As to induction and deduction, vide The Natural History of 

 Creation. 



