SENSE OF TOUCH. 



859 



termed by Dr.- Graves " the limit of confusion." 

 the results of his experiments : 



The following are some of 



Point of tongue . . . J of a line. 

 Palmar surface of third phalanx 1 line. 

 Red surface of lips . . .2 lines. 

 Palmar surface of second phalanx 2 

 Dorsal surface of third phalanx 3 

 Palmar surface of metacarpus 3 

 Tip of the nose . . .3 

 Dorsum and edge of tongue . 4 

 Part of lips covered by skin . 4 

 Palm of hand . . .5 



Skin of cheek . . .5 

 Extremity of great toe . . 5 

 Hard palate . . . .6 

 Dorsal surface of first phalanx 7 

 Dorsum of hand . . .8 



Mucous membrane of gums 

 Lower part of forehead 

 Lower part of occiput 

 Back of hand . 

 Neck, under lower jaw 

 Vertex . . . . 

 Skin over patella 



Dorsum of foot < 

 Skin over sternum 

 Skin beneath occiput 

 Skin over spine, in back 

 Middle of the arm 

 thigh . 



9 lines. 

 10 

 12 

 14 

 15 

 15 

 16 

 18 

 18 

 18 

 20 

 24 

 30 

 30 

 30 



It is curious that the distance between the legs of the compasses 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 dorsum 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 observations, most accurately recognized at the parts 

 which were determined to be most sensible by the foregoing method of inquiry. 1 

 865. As already stated ( 855), the only idea communicated to our minds 

 by the sense of Touch, when exercised in its simplest form, is that of Resist- 

 ance; and it is by the various degrees of resistance which the sensory surface 

 encounters, of which we partly judge by the muscular sense ( 750), that we 

 estimate the hardness or softness of the body against which we press. It is 

 only when either the sensory surface or the substance touched is made to change 

 its place in regard to the other, that we obtain the additional notion of extension 

 or space; this also being derived from the combination of the muscular with the 

 tactile sense. By the impressions made upon the papillae, during the move- 

 ment of the tactile organ over the body which is being examined, the rough- 

 ness, smoothness, or other peculiar characters of the surface of the latter are 

 estimated. Our knowledge of form, however, is a very complex process, requir- 

 ing not merely the exercise of the sense of touch, but also great attention to 

 the muscular sensations. It is chiefly, as formerly remarked, in the variety of 

 movements of which the hand of Man is capable, that it is superior to that of 

 any other animal ; and it cannot be doubted that the sense of Touch, thus em- 

 ployed, affords us a very important means of acquiring information in regard to 

 the external world, and especially of correcting many vague and fallacious 



1 See his Memoir "De Pulsu, Respiratione, Auditu, et Tactu," Lipsise, 1834. This 

 method of inquiry has been since pursued by M. H. Belfield-Lefevre ("Recherches sur la 

 Nature, la Distribution, et 1'Organ du Sens Tactile," Paris, 1837), and by Prof. Valentin 

 ("Lehrbuch der Physiologic des Menschen," band ii. \ 566), with the same general 

 results. It was found by Prof. Valentin, however, that a considerable amount of indi- 

 vidual variation exists in regard to the "limit of confusion;" some persons being able to 

 distinguish the points at one-half or even one-third of the distances -required by others. 

 In the Author's article "Touch" in the "Cyclopaedia of Anatomy and Physiology," vol. iv. 

 p. 1169, will be found a Table including the whole series of observations made by Profrs. 

 Weber and Valentin, the maxima, and minima of the latter being stated, as well as the 

 means. 



