SENSE OF TOUCH. 



727 



being, however, always left between the innermost one and the extremity of 

 the nerve, in which a fluid or semifluid substance is contained. As the " cor- 

 pusmla taetus" and " Pacinian bodies" are only to be found in the papillae 

 of those parts which are distinguished for acuteness of tactile sensibility, we 

 cannot regard them as essential to the exercise of the sense of touch ; their 

 function, either being to intensify tactile impressions, where delicacy of touch 

 is peculiarly required, 1 or perhaps to supply information in regard to varia- 

 tions in the strength of certain stimuli, as those of temperature or pressure. 



594. The relative sensibility of different parts of the Skin may be in some 

 degree judged of by the results of the observations of Prof. E. H. Weber; 2 

 whose mode of ascertaining it was to touch the surface with the legs of a 

 pair of compasses, the points of which were guarded with pieces of cork, 

 and then (the eyes being closed) the legs were approximated, until they were 

 brought within the smallest distance at which they could be felt to be dis- 

 tinct from one another, which has been termed by Dr. Graves " the limit of 

 confusion."- -The following are some of the measurements taken : 



of a line. 



Point of tongue, . . . . 

 Palmar surface of third pha- 



lanx, ....... 1 line. 



Red surface of lips, ... 2 lines. 

 Palmar surface of second 



phalanx, ...... 2 " 



Palmar surface of metacar- 



pus, ........ 3 " 



Tip of the nose, .... 3 " 



Dursum and edge of tongue, 4 " 



Part of lips covered by skin, 4 " 



Palm of hand, ..... 5 " 



Skin of check, ..... 5 " 



Extremity of great toe, 5 " 



Hard palate, ...... 6 " 



Dorsum of hand, .... 

 Mucous membrane of gums, 

 Lower part of forehead, . 

 Lower part of occiput, . . 



Back of hand, 



Vertex, 



Skin over patella, .... 



" sacrum, .... 



" acromion, . 



Dorsum of foot 



Skin over sternum, 

 Skin beneath occiput, 

 Skin over spine, in back, . 

 Middle of the thigh, . . . 



8 lines'. 



9 " 

 10 " 

 12 " 



14 " 



15 " 



16 

 18 " 

 18 " 

 18 " 



24 

 30 



30 



II 

 II 



It is curious that the distance between the legs of the compasses, as well as 

 the rapidity of their motion when they were lightly drawn over the skin, 

 seemed to be greater (although really so much less), when it was felt by the 

 more sensitive parts, than when it was estimated by parts of less distinct 

 sensibility. With the extremities of the fingers and the point of the tongue 

 the distance could be distinguished most easily in the longitudinal direction ; 

 on the dqrsum of the tongue, the face, neck, and extremities, the distance 

 could be recognized best when the points were placed transversely. As a 

 general fact, it seems that the sensibility of the trunk is greater on the 

 median line both before and behind, and less at the sides. Differences in 

 the temperature and weight of bodies were, according to Prof. Weber's ob- 

 servations, most accurately recognized at the parts which were determined 

 to be most sensible by the foregoing method of inquiry. 3 It has been since 



1 In proof of which, various ingenious experiments have been made by Krause (see 

 Zeitschrift fiir Eat. Med., xvii, p. 278). He explains tbeir presence in the mesentery 

 of the Cat as connected with the mechanism and arrangement of the viscera required 

 for the act of springing. 



2 For similar experiments performed by Dr. Ballard, see Lnncet, 1802, vol. i, p. 

 303. Dr. Ballard found that in the hand the tip of the index finger was the most, the 

 dorsal surface of the base of the fifth metacarpal bone the least, sensitive part; the 

 limit of confusion in the former being 0.35 of a line, in the latter 5 lines. 



3 See bis Memoir, De Pulsu, Respiratione, Auditu, et Taclu, Lipsise, 1834. See 

 also Refherches sur la Nature, la Distribution, et 1'Organe du Sens Tactile, by M. H. 

 Bel field -Leffev re, Paris, 1837; and Prof. Valentin's Lehrbuoh der Physiologic des 

 Menschen, Bd. ii, 56ti. In the Author's article, Touch, in the Cyclopaedia of Anat- 



