I 



10412 



THE SENSES 



withdrawn from or imparted to the cutaneous tissues with sufficient 

 abruptness, a sensation of cold or warmth is experienced. And 

 when two portions of the skin at different temperatures are put in 

 contact, we feel that, relatively to one another, one is warm and 

 the other cold. But it is worthy of remark that it is only difference 



of temperature (or, perhaps, rather the 

 rate at which heat is being gained or 

 lost by the skin), and not absolute 

 height, which we are able to estimate 

 by our sensations. Thus, a hand which 

 has been working in ice-cold water will 

 feel water at 10 C. as warm ; whereas it 

 would appear cold to a warm hand. 



Blix, Goldscheider, and others have 

 shown that the whole skin is not en- 

 dowed with the capacity of distin- 

 guishing temperature, but that the 

 temperature sensations are confined 

 to minute areas scattered over the 

 cutaneous surface. The great majority 

 of these are ' cold ' spots i.e., respond 

 to stimulation only by a sensation of 

 cold while a smaller number are 

 ' warm ' spots, and respond only by a 

 sensation of warmth (Fig. 442). These 

 spots can be mapped out by bringing 

 into contact with the skin small pieces 

 of wire at a temperature a few degrees 

 above or below that of the skin. With 

 such mild stimuli a response can 

 generally be obtained only from one 

 kind of spot that is, the cold wire 

 stimulates only the cold and not the 

 warm spots, and vice versa but with 

 much more intense thermal stimuli 

 say, temperatures of 45 to 50 C. 

 not only do the warm spots respond 

 with the appropriate sensation, but 

 the cold spots respond with a sensation 

 of cold. This is well seen when a 

 beam of sunlight is focussed succes- 

 sively on a warm and a cold spot. Inadequate stimuli (mechanical 

 and electrical) also evoke the specific response of warmth from 

 warm spots, and of cold from cold spots. 



When the hand is put into water at the temperature of the skin, 

 and the water slowly heated, the warm spots are at first alone stimu- 



Fig. 442. ' Warm ' and ' Cold ' 

 Areas on Skin (Goldscheider). 

 The areas are mapped out on 

 the palm of the left hand. In 

 the upper figure the relative 

 sensitiveness to warmth is 

 represented by the depth of the 

 shading, the black areas being 

 most sensitive, then the lined 

 areas, then the dotted, and 

 last of all the white areas. In 

 the lower figure the relative 

 sensitiveness to cold stimuli is 

 shown in the same way. 



