CHAPTER XY, 



THE SENSES. 



THE senses are five in number, namely, common sensation 

 and the four special senses; and the special senses are natiir- 

 ally arranged in two pairs, taste and smell giving sensations 

 of a simple kind, while the sensations of sight and hearing 

 are of a far more complex description, and produced by the 

 action of exceedingly complex organs. 



159. Common Sensation includes feeling and touch. In 

 feeling, the mind has simply the idea of a condition of the 

 body; while from touch it receives an idea of properties of 

 external objects. Pain, tickling, and a sense of warmth or 

 cold are instances of feeling which are not necessarily accom- 

 panied with touch. 



Although the variety of common sensation constituting touch 

 is confined to the surface of the body and to the mouth, and the 

 skin, with its nerve terminations, already described (p. 68), is 

 the principal organ of this sense, feeling is not confined to the 

 surface. Pain, as we all know, may be felt in the deep 

 parts; and there is another form of feeling in deep tissues 

 which has excited a good deal of attention, namely, muscular 

 sense. Although the mind is unconscious of the particular 

 muscles which exist in any part, it is yet able to regulate 

 their contraction, so as to produce and direct every move- 

 ment with precision, which it could not do without a know- 

 ledge of the position of the parts. No doubt this knowledge 

 is only partly due to a sense of the state of the muscles, as 

 may be illustrated by the consideration that in moving one's 

 fingers there is little sense of action save in the fingers them- 

 selves, although we know that the muscles which flex and 

 extend the fingers are really in the forearm; but we can 

 make the muscles of a limb rigid by an effort of the will 



