184 THE HUMAN BODY 



sensations which leads us to form ideas concerning the existence, 

 form, position, and properties of external things. Such represen- 

 tations as these, founded on our senses, are called perceptions. 

 Since these always imply some mental activity in addition to a 

 mere feeling, their full discussion belongs to the domain of Psy- 

 chology. Physiology, however, is concerned with them so far as 

 it can determine the conditions of stimulation under which a 

 given mental representation concerning a sensation is made. 

 It is quite certain that we can feel nothing but states of ourselves, 

 but, as already pointed out, we have no hesitation in saying we 

 feel a hard or a cold, a rough or smooth body. When we look at 

 a distant object we usually make no demur to saying that we 

 perceive it. What we really feel is, however, the change produced 

 by it in our eyes. There are no parts of our Bodies reaching to 

 a tree or a house a mile off and yet we seem to feel all the while 

 that we are looking at the tree or the house and feeling them, and 

 not merely experiencing modifications of our own eyes or brains. 

 When reading we feel that what we really see is the book ; and yet 

 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 sensitive 

 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 comes in contact with 

 the table. A blind man gropes his way along by feeling at the end 

 of his stick. 



