SENSE OF TOUCH. 



753 



Table of Variations in the Tactile Sensibility of Different Portions of the 

 Skin (Weber and Valentin). 



The tactile sensibility is measured by the greatest distance between two points at which they convey a single 

 impression when applied simultaneously. The measurements are given in lines (^ of an inch). 



Titillation. The sensation experienced when certain parts of the general surface are 

 subjected to titillation cannot easily be described, although it is sufficiently familiar. This 

 sensation is due simply to delicate impressions made in unusual situations and is remark- 

 able chiefly on account of the reflex movements which it occasions. If the soles of the 

 feet be tickled, it is almost impossible to avoid movements of the limbs. These are not 

 due entirely to the peculiar sensation appreciated by the brain, for the same stimulus, in 

 persons suffering from complete paralysis of sensation and voluntary motion of the lower 

 extremities, may produce even violent action of the paralyzed muscles. The peculiar 

 48 



