SENSE OF TEMPERATURE 



635 



Sense of Temperature. The whole surface of the body is more or 

 less sensitive to differences of temperature. The sensation of heat is distinct 

 from that of touch, hence it would seem reasonable to suppose that there are 

 special nerves and nerve endings for temperature. At any rate the power of 

 discriminating temperature may remain unimpaired when the sense of touch 

 is temporarily in abeyance. Thus if the ulnar nerve be compressed at the 

 elbow till the sense of touch is very much dulled in the fingers which it sup- 

 plies, the sense of temperature remains quite unaffected. And in certain 

 diseases of the cord the sense of touch may be impaired in a part, and tem- 

 perature remain undisturbed, or the converse. 



The mapping of the surface of a part of the skin with reference to its 

 sensibility to temperature reveals the fact that there are definite heat and 



FIG. 421. Diagram of a Part of the Hand, Showing Distribution of Sense Spots; for 

 touch, A ; for heat, B\ and for cold, C. In A the skin is sensitive except at the parts marked 

 \vith black; in B and C, the intensity of the shading represents the relative sensitiveness. 

 (Goldscheider.) 



cold spots. Furthermore, the areas do not coincide, leading us to conclude 

 that there are two distinct sense organs concerned, figure 421, B and C. 



The sensations of heat and cold are often exceedingly fallacious, and in 

 many cases are no guide at all to the absolute temperature as indicated by 

 a thermometer. All that we can with safety infer from our sensations of 

 temperature is that a given object is warmer or cooler than the skin. Thus 

 the temperature of our skin is the standard; and as this varies from hour to 

 hour according to the activity of the cutaneous circulation, our estimate of 

 the absolute temperature of any body must necessarily vary too. If we put 

 the left hand into water at 5 C. (40 F.) and the right into water at 45 C. 

 (i 10 F.), and then immerse both in water at 27 C. (80 F.), it will feel warm 

 to the left hand, but cool to the right. Again, a piece of metal which has 

 really the same temperature as a given piece of wood will feel much colder, 

 since it conducts away the heat much more rapidly. For the same reason 

 air in motion feels very much cooler than air of the same temperature at rest. 



In some cases we are able to form a fairly accurate estimate of absolute 



