218 THE HUMAN BODY 



external or internal; a person coming in from a windy walk often 

 feels a room uncomfortably warm which is not really so; the 

 exercise has accelerated his circulation and tended to warm his 

 skin, but the moving outer air has rapidly conducted off the extra 

 heat; on entering the house the stationary air there does this less 

 quickly, the skin becomes hotter, and the cause is supposed to be 

 oppressive heat of the room. Hence, frequently, opening of win- 

 dows and sitting in a draught, with its concomitant risks; whereas 

 keeping quiet for five or ten minutes, until the circulation had 

 returned to its normal rate, would attain the same end without 

 danger. 



The acuteness of the temperature sense is greatest at tempera- 

 tures within a few degrees of 30 C. (86 F.); at these differences of 

 less than 0.1 C. can be discriminated. As a means of measuring 

 absolute temperature, however, the skin is very unreliable, on 

 account of the changeability of its sensation zero. We can 

 localize temperature sensations much as tactile, but not so ac- 

 curately. 



The receptors for cold are near the surface of the skin; those 

 for warmth are embedded deeply within it. While the latter re- 

 spond only to temperatures above their own, the cold receptors 

 are stimulated not only by temperatures below their own but 

 also by temperatures above 45 C. (140 F.). It is for this reason 

 that a sensation of cold is felt when one first steps into a hot bath; 

 the receptors for cold being nearer the surface than those for 

 warmth are stimulated an instant before them. It is said that the 

 sensation of "hot" as distinguished from "warm'' results from 

 simultaneous stimulation of warmth and cold spots by tempera- 

 tures above 45 C. 



The Peripheral Reference of our Sensations. Repeated men- 

 tion has been made of the fact that we refer our external sensa- 

 tions to the outside world; this is only one case of a more general 

 law, in accordance with which we do not ascribe our sensations, 

 as regards their locality, to the brain, where the sensation is 

 actually aroused, but to a peripheral part. With respect to the 

 brain, other parts of the Body are external objects as much as 

 the rest of the material universe, yet we locate the majority of 

 our internal sensations at the places where the sensory nerves 

 concerned are irritated, and not in the brain. Even if a nerve- 



