9 6 4 



CUTANEOUS SENSATIONS. 



These figures confirm the longer reaction period for warmth sensa- 

 tion, that appears to have first been drawn attention to by Herzen. 



The quality of "locality "in thermal sensations. When heat is 

 applied to the skin at separate areas, there is found to be considerable 

 power of "localising" the places of application. The thermal senses 

 of the skin possess, therefore, like the tactile sense, a spatial quality. 

 Rauber 1 investigated the question by placing warmed metal balls in 

 perforated wooden plates, which latter were applied to the skin. He 

 found sensory circles for the " warmth " sense corresponding with 

 Weber's circles for touch. He did not test cold sensations. This has 

 been done by Goldscheider, 2 who has, moreover, worked not with the 

 average liminal distance, but with " cold spots " and " warmth spots." 



With excitation of a cold or a warmth spot, as with that of a touch- 

 spot, there develops, in consciousness, not only a presentation of quality 

 and quantity regarding the stimulus, but also of locality. By applying 

 punctiform stimuli to pairs of cold spots or pairs of warmth spots, a high 

 degree of " local sign " is found to attach to the resultant sensations. 

 Goldscheider found this quality higher for "cold" than for "warmth" spots. 



The origin and use of such refinement of localising power for cold 

 and warm stimuli is difficult to understand. It may be that it is neces- 

 sary in order to obtain perceptions of continuous areas of small dimension. 

 It is to be noted that when a skin surface is excited by heat, the sensation 

 is referred not to a number of individual spots of warmth in the skin, but 

 to a continuous surface, although the area stimulated is made up of a puncti- 

 formly arranged series of sentient places. This is expressed by the overlap 

 of the sensory circles. The more intense the thermal stimulus, the finer the 

 power of localisation (Klug) both for cold and warmth sensations. Two thermo- 

 aesthesiometers at the same temperature, when placed simultaneously on the 

 skin, produce a sensation perceptibly double when they lie nearer together, if their 

 temperature be 5 C. than if it be 20 C. The distance varies little with 

 stimuli between 20 C. and 40 C. The average liminal distance is less with 

 stimuli at 5 C. than with stimuli at 50 C. Beyond that temperature the 

 stimuli become painful. To examine, therefore, whether mere distance of the 

 temperature of the stimulus from that of the skin was the cause of the greater 

 efficiency of the " cold " than of the " warmth " stimulus, Klug applied the two 

 stimuli to the arm in a bath in which its skin-temperature had been lowered. 

 The average liminal distance was then found smaller for stimuli at 50 C. than 

 at 5 C. But the differences obtained in the distance were only small ; and 

 the universally richer distribution of " cold " spots than " warmth " spots, 

 together with Goldscheider's positive results, make it clear that localisation is 

 somewhat finer for the cutaneous "cold" sense than for the cutaneous 

 " warmth " sense. 



An important point, somewhat allied to that of localisation, has been 

 mentioned above, namely, that simultaneous thermal stimuli, if of the same 

 species, e.g. cold, produce reinforcement of the physiological intensity one of 



1 Centralbl.f. d. med. Wissensch., Berlin, 1869, S. 273. 2 Loc. cit. 



