THE SKIN AND COMMON SENSATION 977 



spots. It is certainly a form of common sensation, and as such less comparable 

 with a touch perception than a pain. In it a series of light, painless, mechanical 

 stimuli, applied over a surface of skin, evokes hardly controllable action of 

 muscles ordinarily secure to the will's mastery. This recalls the uncontrollable 

 reaction of so-called volitional muscles under pain. Summation of stimuli, 

 which forms a characteristic part of the process of production of pain, plays 

 also a prominent role in the production of the tickling "feeling." In both 

 occurs, in consequence of summated sensory stimuli, uncontrollable nervous 

 discharge into a muscular field with elements of triple kind, namely, sympa- 

 thetic (cardiac and goose-skin reflex), 1 respiratory, and volitional, the last 

 including characteristically the muscles of emotional expression, — indeed, as all 

 three kinds concurrently react along with the emotion, all may in a sense be 

 termed emotional. The involuntary motor nerves played on are sympathetic, 

 e.g. the pilomotor, sudorific, cardiac, vasomotor, etc. 2 The pulse is altered ; 

 the volume of the arm decreases under pain, that of the brain increases. The 

 semi-voluntary are those of respiration ; the voluntary, those of expression, and 

 those that move the part which is the seat of application of the stimulus. 

 An ordinary " touch " does not in this way, by a touch-perception, affect the 

 visceral, respiratory, and emotional muscles. The two reactions may be briefly 

 contrasted. A touch evokes uncontrollably a perception of some part of the 

 environment, may or may not evoke a movement, and does not affect the 

 visceral and mimetic musculature. A cutaneous pain evokes uncontrollably a 

 movement (of defence), and uncontrollably an emotion with its obligate visceral 

 and mimetic movement of expression ; it may or it may not evoke a perception 

 of the environment, although it evoke a reference to the body itself. 



The central lines of propagation of the disturbance, provoked by 

 ordinary touch on the one hand, and by painful touch or tickling touch 

 on the other, seem therefore different. The latter irradiates into motor 

 paths, other than those to which the former travels ; and even where 

 the directions of the irradiation in the two cases partially lead toward 

 the same centres, these are reached, in the case of tickling and pain, by 

 lines of approach seemingly less open to inhibition from above than 

 those employed by the reactions of pure tactual or thermal order. 



Here may be adduced the well-known observation by Schiff, 3 confirmed by 

 Herzen. 4 If in the lower cervical region the cord be transected, with exclusion 

 of its dorsal columns, each touch or light handling of the skin, behind the 

 segment of transection, calls forth signs that the animal "feels." The rabbit 

 raises its head, moves its " whiskers," opens its eyes, or gives other signs 

 which, taken together, amount to unequivocal evidence. On the other hand, if 

 the touch stimulus be intensified and converted into a painful stimulus, even of 

 the most extreme kind, there is no further response than that evoked at outset 

 by the touch. Similarly, Schiff states, if a nerve trunk be bared and then 

 lightly taken between forceps, there is an initial start, and after that any 

 further pinching or compression of the nerve remains ineffectual. It is argued 

 from Schiff 's observation that " painful " impressions are conducted, not via the 

 long ascending afferent root fibres of the dorsal columns, but via the grey 

 matter. The experiment certainly shows that if Schiff's interpretation of the 

 signs, as indicating touch and pain, be accepted, conduction for the former 

 occurs along the dorsal white columns, and that the evidence of pain remaining 



1 J. Mackenzie, Brain, London, 1893, vol. xvi. 



2 A. Mosso, "Circolazione nel cervello huniano," Milano, 1881 ; "La paura," Milano, 

 1886; Alt". Lehmann, "Die Hauptgesetze d. Gefiihlslebens," Leipzig, 1892; Fere, Rev. 

 Phil., Paris, tome xx. ; E. A. Wright, Brain, London, 1895, vol. xviii. p. 217. 



3 " Physiologie," Lahr, 1858 ; " Recueil des mdm.," Lausanne, 189G, tome iii. 



4 Arch. f. d. ges. Physiol., Bonn, 1886, Bd. xxxviii. ; also, "Elements d. physiol. 

 humaine," par A. Waller, trad, par A. Herzen, Paris, 1898 (note on p. 601). 



VOL. II. — 62 



