THE SKIN AND COMMON SENSATION 997 



protest against the teaching that pain stimuli and pain sensations are 

 agents and reactions lying beyond the sacred pale of " normal " life. 



Having discarded the supposition of separate afferent nerve fibres 

 with their specific end-organs, entrusted specifically with carrying 

 " painful " impressions to a " pain centre," it is finally worth considering 

 what meaning can be still attached to the phrase " pain centre." There 

 might exist such a specific pain centre, to be reached by currents of 

 overflow from other sense centres, when the violence of their inner 

 excitement had surpassed a certain pitch. Or, again, a certain extreme 

 degree of inner excitement might superimpose the feeling of pain upon 

 the sensation elaborated by each of the sense centres itself, 1 although 

 unequally in degree in the centres of the different senses. 



The rate at which agreeableness and disagreeableness vary with intensity 

 of a sensation, may roughly be represented by a curve about a horizontal line 

 marking the threshold of sensibility. If below the line be disagreeable, the 

 curve at starting from the horizontal rises, at first more slowly than sensational 

 intensity, then faster, and reaches its maximum distance above, that is, on the 

 agreeable side of neutrality, before sensation is near its acme. After its 

 maximum the agreeableness soon drops and sinks below the horizontal zero 

 level into the realm of the disagreeable or painful. Into this it plunges, 

 becoming, after a certain depth, finally asymptotic to the horizontal level. For 

 some sensations — as bitter, sour, and certain smells — the curve does not ascend 

 at all, but enters the realm of disagreeable from its outset. Among these 

 sensations must be included those from the pain spots of the skin. The 

 sensation of pain spots seems to resemble most nearly in this respect such 

 olfactory sensations as in highly osmatic animals certain odours, e.g. that of 

 the skunk, evoke. How intimately vexation of the stream of consciousness by 

 pain stands in relation to intensity of the stimulus, is no way shown better 

 than by simply increasing the number of nerve fibres, under application of a 

 stimulus non-painful when at work upon a limited number. Minuteness of 

 local application of stimuli to the skin does not appear to have yet reached a 

 degree at which it becomes probable that the sensation is caused by excitation 

 of a single nerve fibre alone. The nerve fibres to the skin are in their distribu- 

 tion very intermingled. I found that in most regions of skin, every, even small 

 area, obtains nerve fibres from two successive spinal roots, and in not a few 

 regions of skin the number of spinal roots furnishing the areas is three. 2 

 Hence in a skin field where only one root remains, punctiform stimulation at 

 the field's edge is less bound up with pain than that nearer the field's centre, 

 the latter implicating a greater number of nerve fibres. In regard to the pain 

 produced by cold and warm stimuli size of the skin-surface, i.e. the number of 

 the sensifacient nerve-endings influences in the directest manner the product 

 of the sensation. A finger-joint can be kept comfortably in water at 48° "7 C, 

 but the whole hand plunged into the same water soon becomes painful. 

 Similarly with water at 6° '2 C. The "touch spots" in a skin area do not 

 work all from the same sensibility limen ; increase of pressure on the same 

 field will, within limits, excite fewer touch-organs if light than if heavier. 



That the seat of the neurosis underlying the painful in a sensation is 

 not identical with that of the production of the regular form of the 

 sensation, seems shown by the evidence given of the difference of the 

 central paths of conduction for pain and for touch. The grounds were 

 given above for the belief that the pain-path involves especially the 

 spinal grey matter and the white matter immediately abutting upon 

 that. In connection with this is the prominent part which summation 

 plays in the production of pain. 



1 Lotze, "Med. Psychol.," S. 215 ff. - Phil. Trans., London, 1892. 



