TEMPERATURE SENSATIONS. 563 



suddenly it is produced; touching a metallic body, which 

 conducts heat rapidly to or from the skin, causes a more 

 marked hot or cold sensation than touching a worse con- 

 ductor, as a piece of wood, of the same temperature. 



The change of temperature in the organ may be brought 

 -about by changes in the circulatory apparatus (more blood 

 flowing through the skin warms it and less leads to its cool- 

 ing), or by temperature changes in gases, liquids, or solids in 

 contact with it. Sometimes we fail to distinguish clearly 

 whether the cause is 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 circula- 

 tion 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 docs this less quickly, the 

 skin gets hot, 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 

 temperatures within a few degrees of 30 0. (86 F.); at 

 these differences of less than.lC. can be discriminated. 

 As a means of measuring absolute temperatures, however, 

 the skin is very unreliable, on account of the changeability 

 of its sensation zero. We can localize temperature sensa- 

 tions much as tactile, but not so accurately. 



Are Touch and Temperature Sensations of Different 

 Modality ? Tactile and temperature feelings are ordina- 

 rily so very different that we can no more compare them 

 than luminous and auditory; and if we accept the modern 

 modified form of the doctrine of specific nerve energies 

 (p. 191), in accordance with which the same sensory fibre 

 when excited always arouses a sensation of the same quality 

 because it excites the same brain-centre, it is hard to con- 

 ceive how the same fibre could at one time arouse a tactile, 

 and at another a temperature sensation. It has, however, 

 been maintained that touch and temperature feelings 



