THE SENSES. 551 



is moderately thin. When its thickness is much increased, as over the 

 heel, the sense of touch is very much dulled. On the other hand, when 

 it is altogether removed, and the cutis laid bare, the sensation of contact 

 is replaced by one of pain. Further, in all highly sensitive parts, the 

 papillae are numerous and highly vascular, and usually the sensory 

 nerves are connected with special End-organs. 



The acuteness of the sense of touch depends very largely on the 

 cutaneous circulation, which is of course largely influenced by external 

 temperature. Hence the numbness, familiar to every one, produced by 

 the application of cold to the skin. 



Special organs of touch are present in most animals, among which 

 may be mentioned the antennas of insects, the "whiskers" (vibrissae) of 

 cats and other carnivora, the wings of bats, the trunk of the elephant, 

 and the hand of man. 



Judgment of the Form and Size of Bodies. By the sense of touch the 

 mind is made acquainted with the size, form, and other external charac- 

 ters of bodies. And in order that these characters may be easily ascer- 

 tained, the sense of touch is especially developed in those parts which 

 can be readily moved over the surface of bodies. Touch, in its more 

 limited sense, or the act of examining a body by the touch, consists 

 merely in a voluntary employment of this sense combined with movement, 

 and stands in the same relation to the sense of touch, or common sensi- 

 bility, generally, as the act of seeking, following, or examining odors, 

 does to the sense of smell. The hand is best adapted for it, by reason 

 of its peculiarities of structure, namely, its capability of pronation and 

 supination, which enables it, by the movement of rotation, to examine 

 the whole circumference of the body; the power it possesses of opposing 

 the thumb to the rest of the hand, and the relative mobility of the fin- 

 gers; and lastly from the abundance of the sensory terminal organs 

 which it possesses. In forming a conception of the figure and extent of 

 a surface, the mind multiplies the size of the hand or fingers used in the 

 inquiry by the number of times which it is contained in the surface tra- 

 versed; and by repeating this process with regard to the different dimen- 

 sions of a solid body, acquires a notion of its cubical extent, but, of 

 course, only an imperfect notion, as other senses, e. g., the sight, are 

 required to make it complete. 



Acuteness of Touch. The perfection of the sense of touch on differ- 

 ent parts of the surface is proportioned to the power which such parts 

 possess of distinguishing and isolating the sensations produced by two 

 points placed close together. This power depends, at least in part, on 

 the number of primitive nerve-fibres distributed to the part; for the 

 fewer the primitive fibres which an organ receives, the more likely is it 

 that several impressions on different contiguous points will act on only 



