460 



THE SENSORY FUNCTIONS OF THE SKIN 



The temperature sense is about equally developed at symmetrical points on 

 the two sides of the body, but there is no special congruence exhibited between 

 such points. 



The mucous membranes possess as a rule but a feebly developed temperature 

 sense, or, as is true of the cornea, none at all. Especially is the heat sense poorly 

 developed in such places. 



A given cold stimulus will evidently produce a greater cooling in a unit of 

 time and will therefore constitute a stronger stimulus for the cold nerves, on 



a. Cold sense. 



ota- Spat inter Os meta- Spatiun 

 ni ofseum carpi inter- ofseum Ls met a 



carp, /; Sp at 



b. Warm sense 



n- -smeta- Spat inter- 



FIG. 183. Topographical distribution of the cold and heat senses over the middle region of the 

 back of the hand, after Goldscheider. The relative sensitivity is indicated by depth of shade. 



parts of the body which are ordinarily clothed than on unclothed parts. The 

 relation of the heat sense to the cold sense is for this reason somewhat different 

 on clothed and unclothed parts. 



So long as the temperature of the surrounding atmosphere changes but 

 little, we do not as a rule experience any sensation of temperature, although 

 some parts of the skin, according as they are clothed or not, may be very 

 much warmer or colder than others. When a person goes from one room 

 in which he feels neither cold nor warm into another which is colder (or 

 warmer), he immediately feels cold (or warm). But if the difference between 

 the two rooms is not very great, all sensations of temperature disappear within 

 a short time. If now he returns to the first room, his experience of tem- 

 perature will be just the reverse of the former change, until again the sensa- 

 tion gradually wears off. 



The temperature of the surrounding atmosphere therefore may vary within 

 certain limits without producing in us any corresponding sensation. One 

 might suppose that this ability of the skin to adapt itself to slight changes 

 of temperature would be due to variations in the distribution of blood, so 



