CH. LL] SENSATION 715 



Partly through congenital, partly through acquired experience, 

 the brain refers the sensation to the nerve-ending which received 

 the stimulus; thus pain in the finger is referred to the finger, 

 the sight of an object to the eyes, etc. If the ulnar nerve is 

 stimulated by a knock on the elbow, the sensation is referred to 

 the fingers where the nerve is distributed ; if the stump of a recently 

 amputated leg be stimulated, the brain not having got used to the 

 new condition of things, refers the sensation to the toes, which still 

 seem to be present. 



Perception is a more complicated mental process ; it consists in 

 the grouping of sensations, and the imagining of the object from 

 which they arise, and which is called the percept. The smell, the 

 taste, the colour, etc., of an orange are all sensations ; the grouping 

 of these together constitutes the perception of an orange. Each 

 mental process leaves an impress on the mind ; these impressions 

 build up memory, or representative imagination ; this may be repro- 

 ductive, as in recalling a friend's face ; or constructive, as in picturing 

 the face of an historical person. 



During the whole operation, moreover, there must be attention; 

 it is quite possible, for instance, in a dreamy person, that he may 

 look at a thing without seeing it, or be present at a lecture without 

 hearing it. 



The more complex intellectual operations consist in the forma- 

 tion of concepts, and reasoning the grouping and discrimination of 

 conceptions. Just as perception is built up of sensations, so 

 conception is built up of perceptions. Thus the orange of our 

 previous example is learnt to be one of similar substances called 

 fruits ; fruits to be products of the vegetable, as distinguished from 

 the animal world, and so on. 



This is seen in the education of a child : at first scattered sensa- 

 tions only are perceived, and by education he learns what these sensa- 

 tions correspond to in the external world, and how they may be 

 classified. The other mental faculties are in the same way built of 

 simpler material ; from the first, perceptions and conceptions find an 

 outlet in motor activity ; at length the conscious realisation of ideas 

 of movement culminate in the purposeful actions of volition. More- 

 over, every experience contains its own quantum of pain or pleasure, 

 and produces reflex contractions or relaxations in vascular and other 

 tissues, which in their turn possess a painful or pleasurable com- 

 ponent. So, too, ideas acquire their colouring of pain or pleasure, 

 ultimately elaborating the complex emotions of sorrow, joy, etc. 



The nerve-endings that receive the impression from the external 

 world are of various kinds. They may be simply ramifying and 

 interlacing plexuses of nerve-fibrils, as in the cornea, parts of the 

 skin, and in the interior of the body ; this kind of nerve-ending is 



