48 SENSATION AND REACTION 



may feel pain in the toes that he no longer posses- 

 ses, if action in the brain should reproduce 

 twinges that he associated with his toes before 

 his leg was amputated. Our physical sufferings 

 are then, so to speak, all mental, and we locate 

 them in various parts of the body by inferences 

 which are deceptive but are very useful. Pain 

 that arises directly in the brain, in conditions of 

 mental hallucination, may be as acute as when a 

 bodily organ is physically affected. We should, 

 then, think of sensations as created by the brain, 

 not by the organs of sense ; in this respect they 

 resemble memories or hallucinations. Sensations 

 are generally more vivid than memories. But we 

 may at times be at a loss to decide whether a 

 brain picture comes from the outside, or arises, as 

 a vision, within us. 



In the higher animals a sensory apparatus 

 consists, in the first place, of some peculiarly 

 modified tissue on the exterior surface of the 

 body, specially adapted for the reception of 

 outside impressions. Such are the rods and cones 

 of the retina of the eye, the Cortian fibres which 

 line the inner passages of the ear, and the nerve 

 endings by which we gather the impressions of 

 touch and taste. Secondly, it includes a nerve 

 system by which the impression is transmitted 

 to a point where it is converted into an impulse 

 that flies outward to actuate a muscle. In its 

 essential form this system consists of a sensory, 

 or " afferent " nerve, a ganglion, in which this 

 nerve ends, and a motor or " efferent " nerve 

 proceeding from the ganglion to a muscle. By 

 biologists of a materialistic way of thinking, the 

 afferent nerve is pictured as causing a chemical 

 reaction, or explosion, in the ganglion, and as in 

 this manner setting free energy which is stored 

 in the ganglion. But it may also be pictured as 



