976 CUTANEOUS SENSATIONS. 



reckoning upon it. 1 "Economics as a science bases itself upon the conscious 

 choice of pleasure." 2 



Nothing said above disallows of the term " common sensation " being 

 taken to embrace the whole office of the cutaneous senses, touch, cold, 

 warmth, as well as the senses of the musculo-articular apparatus, and 

 of the viscera, on the assumption that all these share in common the 

 incapacity to " project " their sensations, and to provoke, under conditions 

 of excessive stimulation, pain. On such a view the nerves of tactual 

 and thermal sense, under appropriate circumstances, produce cutaneous 

 pain ; and the nerves which furnish the sensory impressions at basis of 

 the perceptions of the " muscular sense " likewise, under appropriate 

 conditions, produce the " ache " of muscular fatigue, the " gnawing " 

 pain of hunger, the " cutting " pains of visceral cramp, etc. So also, on 

 the same view, the feeling of thirst and the pain of cardialgia may both 

 be the manifestations of the same gastric nerve fibres. But on this 

 view the old difficulty encountered above, regarding the specificity of 

 pain, has to be met with again, although in modified form. 



Pain as a skin sensation is sui generis, incapable of confusion with the 

 sensations evoked by other, usually lesser, stimuli. It is not as if some 

 painful component inherent in cutaneous sensation from the limen up- 

 wards increased, and increased disproportionately as the reaction grew 

 more violent. There is no trace of the painful in a moderate " warmth 

 sensation." Though musical notes of different pitch can be confused by 

 a mind not musically trained, there is no chance of confusion in any 

 mind between sensations of, for instance, pure " cold " and " pain." 

 A pain sensation evoked by pressure from the skin does not qua 

 sensation appear to introspection as an intensified touch sensation, 

 though the stimulus for the former may be merely the intenser appli- 

 cation of a contact. The degree of warmth sensation that a burn gives 

 need not be more intense as a sensation of " warmth " than is a painless 

 warmth sensation ; in fact it is often less so, for the new sensation of 

 pain suppresses sensations that might be simultaneously evoked. 



The statement arrived at, therefore, comes to be: If the forms 

 of common sensation as a group be characterised by want of projection 

 and potential pain, among cutaneous sensations are certain which fall 

 into the category of common sensation. The skin, therefore, contributes 

 to common sensation ; that is, nerves of common sensation are dis- 

 tributed to the skin. But it does not conversely follow that all 

 cutaneous nerves are nerves of " common sensation." Are the nerves of 

 common sensation identical with those of touch and warmth and cold, 

 or with one or other among them, or with none of them ? 



The central neural mechanism for cutaneous " common sensation," e.g. 

 pain, is certainly largely distinct from that of touch and temperature. This 

 seems clearly indicated on examining both pain and the " feeling " of tickling. 

 Tickling, it is sometimes taught, results from stimulation of the purely tactual 

 nerves. The mechanism of the matter probably is that weak tactual stimuli 

 call into reflex activity unstriated muscles of the skin. The contraction of these 

 excites the feeling of shivering which combines with that of the light touches. 

 In that case it is conceived to be a peculiar psychical elaboration from 

 tactual and muscular impressions. It may be so, and it may stand in some- 

 what the same relation to the touch spots of the skin as does pain to the pain 



1 See Patten, "Theory of Social Forces," Philadelphia. 



2 Witmer, "Twentieth Century Practice of Medicine," 1897, vol. xi. p. 919. 



