iooo CUTANEOUS SENSATIONS. 



by increase of the extent of the stimulus, i.e. by simple increase of the number 

 of nerve fibres excited (cf. " Cutaneous Senses of Cold and Warmth," p. 956). 



The stimuli which evoke pain may be characterised as " excessive." 

 It might almost be asserted that " excess " is that quality of a stimulus in 

 virtue of which it becomes " adequate " for the sense of pain. " Excess- 

 ive " in this application connotes " harmful," or " to be avoided," e.g. by 

 muscular action for resistance or escape. The " excess " of the stimulus 

 may lie in its intensity, or in its extensity (spatial or temporal). 



The conclusions thus reached may be briefly stated thus : — Affective 

 tone is an attribute of all sensation, and among the attribute tones of 

 skin sensation is skin-pain. Affective tone inheres more intensely in 

 senses which refer to the body than in those which refer to the environ- 

 ment, that is, it is strongest in the non-projicient senses. It is there- 

 fore strong in the cutaneous senses, and in them is inversely as their 

 projicience, therefore least in touch spots, more in thermal spots, most 

 in the so-called " pain spots." The sensations from pain spots have 

 weak tactual quality and strong affective quality, especially of negative 

 tone. The pain produced by heat is probably evoked from " pain spots," 

 and not from thermal spots ; the pain produced from " pain spots " is 

 produced not only by mechanical stimuli, but probably also by thermal, 

 chemical, and electrical stimuli. Stimuli evoking skin -pain are 

 broadly such as injure or threaten injury to the skin ; the skin may be 

 said to have gone far toward developing a special sense of its own 

 injuries. The central conducting path concerned with these skin 

 feelings seems a side-path into which the impressions from the various 

 skin spots embouch with various ease, those from the " pain spots " 

 especially easily. The physiological reactions connected with this side- 

 path are characterised by tendency to " summation," tendency to 

 " collateral irradiation," slow culmination and slow subsidence. They 

 often involve with their own activity that of adjacent sensory channels 

 (associate pains, referred pains), and almost invariably of motor centres 

 of visceral, facial, and other muscles of expression (emotional discharge). 



Can bodily pains be of central nervous origin ? The dog from 

 which the cerebral hemispheres have been removed gives reactions, 

 interpreted 1 as evidencing pain. Budge and others 2 have examined 

 by experiment the effect of stimuli to various parts of the brain, with 

 a view to discovering which parts can give rise to painful sensation, 

 and which not. The result of their observations, chiefly made on 

 the rabbit, has been negative as regards evidence of pain from 

 all parts above the optic thalami. From the optic thalami the evidence 

 was equivocal ; what there was Budge was inclined to attribute to the 

 adjoining cms cerebri. From the corpora quadragemina down to the 

 lower end of the rhomb-encephalon inclusive, signs of pain were easily 

 evoked. Pathology seems to prove the production of pain by irritative 

 lesions of the thalamus. Support is lent by the close connection found 

 clinically :i and experimentally 4 between the thalamus and bodily 

 expression of emotion. 



1 Ooltz, Arch. f. d. ges. Physiol., Bonn, 1892, Bd. li. ; and Munk's critique, Arch. f. 

 Physiol., Leipzig, 1892. 



2 " Untersuch. ueber d. Nervensvstem," 1841, Bd. i. S. 10; "Physiol, d. Menschen," 

 Leipzig, 1862; Schiff, " Physiologic", " Lahr, 1858, Bd. i. S. 242; Lussana, and Lussana 

 and Lemoigne, Arch, de physiol. norm, el path., Paris, 1860 ; Longet, Bechterew, etc. 



3 Nothnagel, Meynert, Rosenhach, Kiritzow, Mingazzini. 



4 Bechterew, Outanskow, Mislawski. 



