254 From Matter to Man. 



The brain, the central organ of man's mind, is thus 

 a machine located in man's larger machine, his body ; 

 a body subordinate in turn to the much larger 

 machine, the world. Hence, as a machine, the brain, 

 and consequently the mind, but registers the motions 

 communicated to it by the other mechanisms of 

 existence, externally and internally associated with 

 it. Outside of these mechanisms and motions the 

 brain cannot act and the mind cannot know. 



Section 2. The Evolution of Human Consciousness : 

 The great physiological problem is consciousness, 

 and the utmost efforts of sane philosophers since 

 philosophy began has been to describe in physical 

 terms the conscious state, so as to say, in such and 

 such acts is consciousness done. The modus operandi, 

 or reflex action of consciousness, is as follows : — A 

 stimulus automatically vibrates a sensory surface ; 

 this vibration in turn automatically ripples as a wave 

 of molecular movement along the sensory nerves to a 

 nerve centre ; this again automatically transmits a 

 wave of molecular movement down a motor nerve to 

 a group of muscles over which it presides ; they 

 automatically contract, and this contraction produces 

 one or other of the thousands or millions of actions 

 known as human consciousness. Or to state the pro- 

 cess differently : — A stimulus from outside applied to 

 a terminal nerve, in, say, the eye, causes molecular 

 changes which result in the transmission of an impulse 

 to the brain. In the brain, molecular changes again 



