924 CUTANEOUS SENSATIONS. 



front of distal end of the forearm. In the toes, on the average, one papilla out 

 of every four contains a corpuscle (Meissner). It is not clear that the so-called 

 " tactile cells" (Merkel) are concerned with touch, but in addition to the Meissner 

 corpuscles there occur in the papillae of the palmar and digital skin the 

 " plume-organs " of Ruffini, so called on account of their shape. 1 These possess 

 a nerve-ending quite different from that of either the simple or the compound 

 Meissner organs ; the network of terminal nerve filaments is much more rich and 

 complex in the " plume-organs," and is not enclosed in such a thick or definite 

 capsule as that of the Meissner organs. Beneath the organs of the papillae there 

 lie at various depths the nerve-endings discovered by Ruffini, 2 the "elastic 

 tissue spindles." Numerous and of wide distribution, these are very probably 

 tactual. Deeper still occur the Golgi-Mazzoni corpuscles, and in some regions 

 fair numbers of Pacini corpuscles. 



The adequate stimulus.— The " touch spots " are found to be the 

 most sensitive points of the skin surface They are readily excited, not 

 only by pushing the skin surface inward, but also by pulling it outward 

 (v. Frey). When of small amplitude, a push at a touch spot cannot be 

 distinguished from a pull of equal amplitude. Meissner 3 years ago 

 pointed out that the hand immersed in a fluid at body temperature 

 fails to feel the contact of the fluid, although the fluid pressure may be 

 far above that of liminal intensity for touch. It seems clear that the 

 adequate stimulus for touch organs consists in deformation of the skin 

 surface. Fluid exerting everywhere a pressure normal to the face of 

 the submerged skin does not deform the surface, except at a boundary 

 of submerged and unsubmerged parts. At that boundary it is, as 

 Meissner observed, felt. Elsewhere it bears on the sides as on the 

 summits of the skin ridges equally. On the contrary, a solid surface 

 presses primarily on the ridge summits and not on the ridge sides. 

 The solid, therefore, causes deformation, and its contact stimulates the 

 tactual surface, and is perceived. 



A bristle attached to the prong of a vibrating tuning-fork can be 

 used for stimulating a " touch spot " intermittently. The resulting 

 sensations retain a quality of intermittence, even at high frequency of 

 repetition of the stimulus. The vibrations of strings are recognisable 

 as such by the finger, even at a frequency of 1552 vibs. per second. 4 

 Induced currents evoke distinctly intermitting sensation, at a repetition 

 of 130 per second. 5 A wheel with toothed edge gives sensation of 

 smoothness at its edge when the teeth meet the skin in succession 

 at the rate of 480 to 640 per second. 6 As compared with the sensation 

 obtained from pain spots, " touch " is quicker both of development and 

 subsidence. 7 



1 Monitorc zool. ital., 1895, tomo vi. p. S ; " Di nuove forme d. termin. nerv. n. strato 

 pap. e. subpap. d. cute," Siena, 1898. 



2 Atti. d. r. Accad. d. Lined. CI. di sc. fis., mat. c nat., Roma, 1893, tomo vii. ; and 

 " Ulteriori ricerche sugli organ, nerv. term. n. conn, sottocut. d. polpast. d. uomo., 

 Ricerche u. lab. di anat. norm. d. r. Univ. di Roma, 1896, tomo v. fasc. 3 ; Sfameni, 

 Anat. Anz., Jena, Bd. ix. S. 22. 



3 Ztschr.f. rat. Med., Dritle Reihe, Bd. vii. S. 92. Meissner farther relates that when 

 a very accurately cast mould of the finger, made in paraffin, is carefully reapplied, it 

 excites no " touch," except at its margin. 



4 Landois, "Lehrbuchd. Physiol, d. Menschen," 1880 ; Preyer, "Empfindungsvermogen," 

 Bonn, 1866. 



5 v. Frey, loc. cit. Of. Bloch, Trar. du lab. dc Marey, Paris, 1897. 



6 Valentin, Arch. f. physiol. Heilk., Stuttgart, 1852, pts. 3 and 4, Bd. xi. ; Sergi, Ztsehr. 

 f. Psychol, u. Physiol, d. Sinnesorg., Hamburg u. Leipzig, 1892, Bd. iii. 



7 Goldscheider, loc. cit. ; Nngel, loc. cit.; v. Prey, loc. cit. 



