430 INNERVATION. [CHAP. xiv. 



of the chief segments, the arm, fore-arm,, thigh, and leg. The con- 

 vexities of the joints are more sensible than the concavities. 



The hand and foot greatly excel the arm and leg, and the hand 

 the foot. The palms and soles respectively excel the opposite 

 surface, which are even surpassed by the lower parts of the fore- 

 arm and leg. On the palmar aspect of the hand the acuteness of 

 the sense corresponds very accurately with the development of the 

 rows of papillae ; and where these papillae are almost wanting, as 

 opposite the flexions of the joints, it is feeble. 



The scalp has a blunter sensibility than any other part of the 

 head, and the neck does not even equal the scalp. The skin of the 

 face is more and more sensible as we approach the middle line ; 

 and the tip of the nose and red part of the lips are acutely so, and 

 only inferior to the tip of the tongue. This last, in a space of a 

 few square lines, exceeds the most sensitive parts of the fingers ; 

 and points of contact with it may be generally perceived distinctly 

 from one another, when only one-third of a line intervenes between 

 them. As we recede from the tip along the back or sides of the 

 tongue, we find the sense of touch much duller. 



The sensibility of the surface of the trunk is inferior to that of 

 the extremities or head. The flanks and nipples, which are so 

 sensitive to tickling, are comparatively blunt in regard to the ap- 

 preciation of the distance between points of contact. Points placed 

 on opposite sides of the middle line, either before or behind, arc 

 better distinguished than when both are on the same side. 



The above are the results obtained by making the several parts 

 mere passive and motionless recipients of impressions. They evince 

 the precision of the sense in so far only as it depends on the organi- 

 zation of the tactile surface. The augmented power derived from 

 change of position of the object with regard to the surface, is well 

 illustrated by keeping the hand passive, while the object is made to 

 move rapidly over it. In this case the contact of the two points is 

 separately perceived, when so close, that they would, if stationary, 

 seem as one. If, still further, the fingers be made to freely traverse 

 the surface of an object, under the guidance of the mind, the appre- 

 ciation of contact will be far more exquisite, in proportion to the 

 variety of the movements, and the attention given to them. We 

 are then said to feel, or to examine by the sense of touch. 



How great is the aid thus capable of being afforded, is manifest 

 in the following experiment. With shut eyes, and the hand still, 

 let another apply to the finger various articles, such as books, paper, 

 glass, metals, wood, cork, &c. ; they will be very imperfectly dis- 



