MENTAL EVOLUTION OF MAN 235 



dominant element of thought. This current is affected 

 by the messages brought to the brain by nerves from 

 the outer parts of the body where he the eye and ear 

 and other sense-organs. In hke manner the various 

 non-nervous parts of the body exert their influences 

 upon consciousness, but the affective processes, as they 

 are called, are not as well understood as the impressions 

 passed inwards by the sense-organs along their nervous 

 roadways to the central organ, the brain. But the 

 brain is the place where the thinking individual re- 

 sides ; and this is one of the most important teachings 

 of psychology, for not only does it help us to under- 

 stand the evidence that human faculty has evolved, 

 but it also inevitably brings us to consider certain vital 

 questions of metaphysics, such as the immortahty of 

 the thinking individual after the material person with 

 its brain ceases to exist. However, the latter question 

 is something which does not concern us here; now it 

 is most important to reahze how completely mind is 

 connected with the brain. 



Many of the facts demonstrating this connection are 

 matters of common knowledge. In deep and dream- 

 less sleep the essential tissues of the brain are inactive, 

 and in correspondence with the cessation of material 

 events the thinking individual actually ceases to exist 

 for a time. Any one who has ever fainted is subse- 

 quently aware of the break in the current of human 

 consciousness when the blood does not fully supply the 

 brain and this organ ceases to function properly; a 

 severe blow upon the head likewise interrupts the 

 normal physical processes, and at the same time the 

 mind is correspondingly affected. Again, a progressive 



