LIMINAL DIFFERENCES FOR THERMAL SENSITIVITY. 961 



to the environment of the moment. For another medium, on contact 

 with it, to elicit from it no sensation either of cold or of warmth, 

 that medium must be of what Hering calls its " adequate tempera- 

 ture." The temperature of the skin being different in different 

 regions, and of different thermal conductivity in different regions, 

 these physical differences, apart from others of physiological nature, 

 necessitate a different " adequate temperature " for media applied 

 at different skin-regions. The distance of the thermal stimuli 

 employed by Weber from the adequate temperature of the part 

 examined, he did not ascertain. It must have varied considerably. If, 

 therefore, the Weber law hold good in any degree for intensity of 

 thermal stimuli, as for intensity of other adequate stimuli, the estima- 

 tions of thermal sensibility, carried out by his method of difference 

 between thermal stimuli, cannot be properly exact when the " adequate 

 temperatures " are disregarded. 



Nothnagel l also examined the degree of thermal sensitivity of the skin 

 by a method similar to Weber's ; he also disregarded the " adequate 

 temperatures." He found the eyelids, cheeks, and temples the most sensitive 

 parts of the face ; but he found their sensitivity equalled in the skin of the 

 sides of the abdomen. The least sensitive part of the face he found to be the 

 bridge of the nose. The ventral surface of the chest he found more sensitive 

 below than above, the back less sensitive than the ventral aspect of the trunk. 

 The middle line of the body he found everywhere relatively insensitive. He 

 found the upper arm more sensitive than the forearm, the forearm more 

 sensitive than the hand ; the same diminution of sensitivity in the peripheral 

 direction obtains in the lower limb, but the whole lower limb is less sensitive 

 than the upper. The dorsum of hand and foot he found more sensitive than 

 palm and sole. 2 



The smallest difference perceptible between the temperatures of the metal 

 (copper) discs used by Nothnagel were for different regions of skin examined 

 in different individuals, as follows : 3 



ForSrm '. | f tensor an f d I -2' C. 



Upper arm . | flexor as P ects I 



Back of hand ...... "3 ,, 



Cheek -4-'2 



Temple '4--3 



Chest -4 



Upper part of abdomen (side) . . . *4 ,, 



Palm ) - , o 

 Dorsum of foot j 



Upper front part of abdomen ) - 



Thigh / ' 



Leg (back of) . . . ) .g. 

 Sternum . / 



Leg (skin) . . '7 



Nipple . 



Back, at the side ...... "9 



,, in the middle line . . . 1'2 



Subsequent to the discovery of "cold spots" and "warm spots," 

 similar investigation of the thermal sensitivity of the various regions 



1 Deutsches Arch. f. klin. Mcd., Leipzig, Bd. ii. S. 284. 



2 But compare E. H. Weber's observation, loc. cif., given below, p. 962. 



3 Loc. cit., with some observations by Goldscheider, loc. cit., added. 

 VOL. II. 6 1 



