CUTANEOUS AND INTERNAL SENSATIONS 1093 



. . . The most striking single experience was the intense algesic cold, 

 which occurred when the skin was hyperaesthetic to cold.' Deep 

 sensibility to pressure and pain was not altered. Localization 

 of pressures (of 20 gm.) and discrimination of two pressures (two- 

 point discrimination) remained unaffected. 



This study on the whole confirms that of Trotter and Davies. How- 

 ever, the larger outer or third area defined by the so-called ' stroking 

 outline ' of Trotter and Davies is probably not an area of sensory 

 abnormality at all, but merely an area in which a physical change in 

 the skin, due, e.g., to some interference with the action of the sweat 

 glands, is appreciated by the stroking finger. This follows from the 

 fact that it can be mapped out approximately by an observer who 

 strokes it with his own finger without asking the subject to report his 

 sensations. The results of Boring's investigation are quite opposed to 

 the most essential of Head's conclusions. No evidence was found in 

 favour of Head's distinction between epicritic and protopathic sensi- 

 bility, and weighty evidence against it. There does not seem to be 

 any real necessity in the observed facts for introducing so revolutionary 

 a conception of the nervous system. Nor is it possible to uphold the 

 distinction in any thoroughgoing fashion for all structures. For in- 

 stance, in abdominal operations performed under local anaesthesia it 

 has been seen that the parietal peritoneum is quite insensitive to touch, 

 pressure, and temperature stimuli, including extreme temperatures 

 (Ramstrom), while pain is caused by traction on it. Its sensibility 

 is therefore neither purely epicritic nor purely protopathic in Head's 

 sense. In like manner the mucous membrane of the mouth, in which 

 sensibility only to touch and temperature is present, conforms entirely 

 to neither type. Its sensibility is not alone epicritic, since it responds 

 to extreme temperatures, nor is it purely protopathic, since a pin-prick 

 produces no painful sensation. These terms and the theory associated 

 with them should be dropped. 



Localization of Cutaneous Sensations. We not only perceive the 

 quality and estimate the intensity of sensations of touch, warmth, cold 

 pain, etc., but are able, more or less accurately, to localize the part of 

 the body from which the sensory impressions come. In other words, 

 two impressions from different parts of the body, although identical 

 in quality and intensity, are nevertheless stamped with a distinctive 

 something, which may be called the local sign. This power of localiza- 

 tion is not equal for all portions of the body nor for all kinds of sensa- 

 tions. It is best developed for touch (in the restricted sense), and all 

 the varieties of common sensation are better localized on the skin than 

 in any of the deeper structures. The precise mechanism of the localiza- 

 tion is unknown. But we must suppose that each peripheral area is 

 ' represented ' in the brain, so that the arrival of afferent impulses from 

 it affects particularly the related cerebral area. The brain, therefore, 

 so to speak, associates excitation of a given cerebral area with stimula- 

 tion of the corresponding peripheral area, and thus not only recognizes 

 the quality and quantity of the resultant sensation, but also localizes 

 it; just as a waiter who watches the bell-indicator not only learns how 

 a bell has been rung, whether once or twice, peremptorily or languidly, 

 but also in which room it has been rung. If, to pursue the illustration 

 a little farther, he is aware that two rooms are connected with one 

 bell, but that one of the rooms is scarcely ever occupied, he associates 

 the ringing of the bell with a summons from the other room even when 

 it happens to be rung from the usually vacant room. In like manner 



