THE SKIN AND COMMON SENSATION. 967 



determine the pleasurable ("positive") or displeasurable (" negative ") tone of 

 sensation, among the most powerful are " intensity and duration." x An 

 intense light or a piercing note evoke sensory disturbances of distinctly 

 " negative tone." With the minimal sensation the agreeableness is nil, but 

 that character reaches its maximum before the total sensation is itself by 

 any means maximal. 



Reference is not intended above to the pain in the eye which, apart from 

 visual sensation, can be caused by very strong illumination. That such pain 

 can be caused by light quite apart from any effect upon visual sensation, is 

 proved by its elicitation from totally blind eyes. 2 It is probably a phenomenon 

 allied to photophobia. Photophobia may occur in the totally blind, and is 

 independent of, although influenced by, the retina and optic nerve. The 

 mechanism of " light-pain " and photophobia is not clear : they are phenomena 

 which led E. H. Weber 3 to question whether, recurring to an older view, 

 there are not nerve fibres of common sensation in the optic nerve. 

 Magendie 4 detected no reactions whatever on scratching the retina in 

 mammals, amphibia, or fish, but in birds, body-movements and contraction of 

 the pupil followed regularly. It is noteworthy that retinitis may run its 

 course completely without pain, whereas inflammatory processes of the 

 conjunctiva produce intense photophobia. 



There are, however, certainly other conditions besides mere intensity and 

 duration which can make sensory impressions agreeable and disagreeable. Some 

 sensations of taste, e.g. bitter, sour, certain odours, possess an unpleasant char- 

 acter — a " negative tone " — almost at the limen of the sensible intensity of the 

 stimulus. Here the disagreeableness seems to be allied, not to the intensity, but 

 to the "timbre" or " colour " or quality of the sensation. Among all simple 

 sensations it is in those of the highest and most projicient senses, e.g. sight, 

 that implication of disagreeable and agreeable seems least an obligatory function 

 of the timbre. Hence one may demur when asked to accept affective tone as an 

 immediate quale inherent in all presentation. 5 When of moderate intensity the 

 majority of simple visual sensations do not, in virtue of mere colour, involve 

 apart from complex associative experience — either delight or pain. Such 

 visual sensations are from the present standpoint "neutral." With the sense 

 of hearing it is different. The concord c, e, g, produces a sensation of positive 

 tone, and is as distinctly elicitive of pleasure as are the notes c and d, simul- 

 taneously struck, provocative of urgent disagreeableness, of — as the very name 

 insists — discord. Between its extremes, imbued with " positive " and 

 " negative" tone, the timbre scale (apart from the intensity scale) of sensation 

 extends a neutral zone untinted, so to say, by either pain or pleasure. On 

 this view a pleasant warmth differs from a painful burn, as the affective 

 tone one of colour, e.g. orange, from the affective tone of another colour, e.g. 

 violet, or as that of one complex tone differs from that of another. 



But in accepting the above view, that pain is but a quality of 

 sensation which, under appropriate circumstances of intensity or quality 

 of stimulus, can arise in the domain of any and each sense, certain 

 difficulties are encountered. It must be admitted that pain arises more 

 frequently and more easily and is much more intense in connection 

 with certain senses than with others. If " sense pain," like " local sign," 

 be considered to be a quality of sensation, the admission has to be 

 granted that, although qualities discoverable in a large group of 



1 AVundt's "Grundziige," Leipzig, 1893. 



2 Ph. v. Waltlier, Journ. d. Chir. v. Aiigerih., Berlin, Bd. xxx. S. 360. 



3 Wagner's " Handworterbuch," Bd. iii. Abth. 2, S. 564. 



4 Journ. de physiol. cxp6r., Paris, 1825, tome iv. pp. 180 and 310. 



5 Marshall, Mind, London and Edinb., 1S94, N. S., vol. iii. p. 533 ; and " Pain, Pleasure, 

 and ^Esthetics," London, 1894. 





