630 



SPECIAL SENSES 



that the centre for this sense probably is in the gyrus fornicatus, which 

 is on the mesial surface of the brain, above the corpus callosum. How- 

 ever, Munk and many others locate this centre in the Rolandic area, a 

 part containing several motor centres. These differences of opinion 

 illustrate the evident difficulty of studying tactile sensibility in the infe- 

 rior animals. 



Appreciation of Temperature. As regards the general temperature, 

 the sense is relative and is much modified by habit. This statement 

 needs no explanation. As is well known, what is cold for an inhabitant 

 of the torrid zone would be warm for one accustomed to an excessively 

 cold climate. Habitual exposure also modifies the sense of temperature. 

 Many persons not in the habit of dressing warmly suffer but little in 



Fig. 155. Map showing the relative distribution of the sensitivity to touch, warmth and cold in the 

 palm of the left hand (Goldscheider) . 



" In A, the whole surface is, when tested by a small cork applied by a spring, found of approxi- 

 mately equal sensitivity except in the areas marked black ; these are relatively insensible for touch. 



" In B, the areas of sensitivity to warmth stimuli are represented by degrees of shading, the most 

 sensitive, by the black shading ; the next, by the lined areas ; the next, by the dotted areas ; and those 

 of least sensitiveness, by the blank spaces. 



" In C, the topography of sensitivity to cold stimuli is indicated in the same way as that to warm 

 'stimuli in B," 



extremely cold weather. Those who habitually expose the hands or 

 even the feet to cold, render these parts comparatively insensible to 

 temperature ; and the same is true of those who often expose the hands, 

 face or other parts to heat. The variations in the sensibility of different 

 parts of the surface to temperature depend, also, on special properties 

 of the parts themselves. 



The experiments of Weber and others show that the skin is the 

 chief organ for the appreciation of temperature, if the mouth, palate, 

 vagina and rectum, by which the differences between warm and cold 

 substances are readily distinguished, are excepted. In several instances 

 in which large portions of the skin were destroyed by burns and other 

 injuries, experiments have been made by applying spatulas of different 



