THE SENSES. 163 



sensation of tickling may be produced in many parts of the body, but 

 with especial intensity in the soles of the feet. Among other sensations 

 belonging to this class, and confined to particular parts of the body, may 

 be mentioned those of the genital organs and nipples. 



(a) Touch proper. In almost all parts of the body which have 

 delicate tactile sensibility the epidermis, immediately over the papillae, 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, such as have been described 

 (p. 337, Vol. L). 



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

 neous 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 antennae 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 

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

 ascertained, 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 sensibility, 

 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 supina- 

 tion, 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 fingers; and 

 lastly from the abundance of the sensory terminal organs which it pos- 

 sesses. 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 traversed; 

 and by repeating this process with regard to the different dimensions 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. 



