SENSATION AND SENSE-ORGANS. 501 



the existence of the book is a judgment founded on a state 

 of our Body, which alone is what we truly feel. 



We have the same experience in other cases, for example 

 with regard to touch. 



Hairs are quite insensible, but are imbedded in the sensi- 

 tive skin, which is excited when they are moved. But 

 if the tip of a hair be touched by some external object we 

 believe we feel the contact at its insensible end, and not in 

 the sensitive skin at its root. So, the hard parts of the teeth 

 are insensible; yet when we rub them together we refer the 

 seat of the sensation aroused 'to the points where they touch 

 one another, and not to the sensitive parts around the sockets 

 where the sensory nerve impulse is really started. 



Still more, we may refer tactile sensations, not merely to 

 the distal ends of insensible bodies implanted in the skin, 

 but to the far ends of things which are not parts of our 

 Bodies at all; for instance, the distant end of a rod held 

 between the finger and a table while the finger is moved a little 

 from side to side* We then believe we feel touch or pressure 

 in two places; one where the rod touches our finger, and the 

 other where it conies in contact with the table. A blind 

 man gropes his way along by feeling at the end of his stick. 

 If the rod is attached immovably to the table we feel only 

 its end next the finger. If we could fix it immovably on the 

 finger while the other end was movable on the table, we 

 would lose the sensation at the finger and refer the sensa- 

 tion of pressure to where the rod touched the table. When a 

 tooth is touched with a rod we only feel the contact at its 

 end, unless it is loose in its socket; and then we get two 

 sensations on touching its free end with a foreign body. 



This irresistible mental tendency to refer certain of our 

 states of feeling to causes outside of our Bodies, and either in 

 contact with them or separated from them by a certain space, 

 is known as the phenomenon of the extrinsic reference of our 

 sensations. The discussion of its origin belongs properly to 

 Psychology, and it will suffice here to point out that it seems 

 largely to depend on the fact that the sensations extrinsically 

 referred can be modified by movements of our Bodies. 

 Hunger, thirst, and toothache all remain the same whether 

 we turn to the right or left, or move away from the place we 

 are standing in. But a sound is altered. We may find that 

 in a certain position of the head it is heard more by the 



