TOUCH. TEMPERATURE SENSATIONS. 583 



at different temperatures; the fingers and nose being cooler 

 than the trunk which is covered by clothes, and this, in turn, 

 cooler than the interior of the mouth. The temperature 

 which a given region of the temperature organ has (as 

 measured by a thermometer), when it feels neither hot nor 

 cold is its temperature-sensation zero for that time, and is 

 not associated with any one objective temperature; for not 

 only, as we have just seen, does it vary in different parts of 

 the organ, but also on the same part from time to time. 

 Whenever a skin region passes with a certain rapidity to a 

 temperature above its sensation zero we feel warmth; and 

 vice versa : the sensation is more marked the greater the dif- 

 ference, and the more 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 conductor, 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 circu- 

 lation 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 windows 

 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 tem- 

 peratures within a few degrees of 30 0. (86 F.); at these , 

 differences of less than .1 C. can be discriminated. As a 

 means of measuring absolute temperatures, however, the skin 

 is very unreliable, on account of the changeability of its sen- 

 sation zero. We can localize temperature sensations much 

 as tactile, but not so accurately. 



Are Touch and Temperature Sensations of Different 

 Modality ? Tactile and temperature feelings are ordinarily so 



