972 



A MANUAL OF PHYSIOLOGY 



respond only by a sensation of warmth (Fig. 427) . 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 re- 

 spond with the appropriate sensa- 

 tion, but the cold spots respond 

 with a sensation of cold. This is 

 well seen when a beam of sunlight 

 is focussed successively 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 stimulated, 

 and the sensations of lukewarm and 

 then of warm are experienced. 

 When the temperature of the water 

 reaches 45 C. the quality of the 

 sensation changes to ' hot/ At a 

 still higher temperature the sensa- 

 tion becomes painful or burning. 

 The most probable explanation of 

 these facts is mentioned below 

 (P- 974)- 



It is not only of physiological in- 

 terest, but of practical importance, 

 that most mucous membranes are in 

 represented by the depth of the comparison with the skin but slightly 

 shading, the black areas being sensitive to changes of temperature. 



m/~kC+ c*anci tit7A fnon i-na linoH * _ / i -i 



Only towards the ends of the alimen- 

 tary canal, in the mouth, pharynx, 

 and rectum, and to some extent in 

 the stomach, does a blunted sensi- 

 bility appear. The uterus, too, is 

 quite insensible to moderate heat ; 

 and hot liquids may be injected into its cavity at a temperature higher 

 than that which can be borne by the hand, without causing incon- 

 venience a fact which finds its application in the practice of gynae- 

 cology and obstetrics. It is, indeed, obvious that in the greater 



FIG. 427. '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 



most sensitive, then the lined 

 areas, then the dotted, and 

 last of all the white areas. In 

 the lower figure the relative sen- 

 sitiveness to cold stimuli is 

 shown in the same way. 



