148 THE SENSES. 



How is the acuteness of touch measured ? 



By means of a pair of compasses whose points are blunted. The 

 legs of the instrument are separated, and the distance, between 

 the points which can just be distinguished as two separate con- 

 tacts, measures the sensibility. From the accompanying table it 

 will be seen that the touch is most acute in the tip of the tongue 

 and in the fingers and tips, while in other portions the sense of 

 touch is so vague that two points of contact are not distinguished 

 until they are 2 J in. apart. It is found that the points of the com- 

 passes must be more widely separated when the test is made in the 

 long axis of a limb than when across it. (The table is from Kirke's 

 Handbook} : 



Table of Variations in the Tactile Sensibility of Different Parts. 

 (The measurement indicates the least distance at which the 

 two blunted points of a pair of compasses could be separately 

 distinguished. E. H. Weber.) 



Tip of tongue -^ inch. 



Palmar surface of third phalanx of forefinger . . - 1 - " 

 Palmar surface of second phalanges of fingers . . 



Red surface of under lip 



Tip of the nose 



Middle of dorsum of tongue 



Palm of hand 



Centre of hard palate 



Dorsal surface of first phalanges of fingers .... yV " 



Back of hand 1 " 



Dorsum of foot near toes 1| " 



Gluteal region 1 



Sacral region 1 " 



Upper and lower parts of forearm \\ 



Back of neck near occiput 2 



Upper dorsal and mid-lumbar regions 2 u 



Middle part of forearm 2^ " 



Middle of thigh 2 " 



Mid-cervical region 2 " 



Mid-dorsal region 2| " 



How is touch modified by education ? 



The sense of touch may be greatly educated and specialized. 

 This is seen in many of the arts where great dexterity obtains by 

 reason of an educated touch. The reading raised letters by the 

 blind is a familiar example of educated touch. 



