42 PHYSIOLOGY CHAP. 



According to Sherrington, cerebral cortical lesions in man 

 disturb tactile localisation far more than any other form of 

 cutaneous sensibility ; the patient, in fact, may refer a touch on 

 the hand to the forearm. 



Before discussing the results obtained by various experimenters 

 on the sense of localisation in different regions, it is necessary to 

 point out certain facts that must be remembered in using Weber's 

 aesthesiometer. These are : 



(a) If the two ends of the compass are put down one after 

 the other, instead of simultaneously, the two contacts will be 

 appreciated at a less distance. 



(5) The same occurs if, in estimating the liminal distance at 

 which the compass-ends are separately perceived, the alteration is 

 made from greater to less distances between the points, instead of 

 from less to greater. 



(c) If one of the ends is warmer or colder than the skin the 

 two contacts will be perceived at a less distance than if both 

 points are of the same temperature as the skin. 



(d) Bathing the skin with indifferent fluids increases tactile 

 discrimination, i.e. the discrimination is sharpened. 



(e) If the skin is gently stroked between the two ends of the 

 compass, or electrified with weak currents, one end only will be 

 detected, where both had previously been perceived. 



The following table gives the value in millimetres of the mean 

 liminal distances for perception of the two points of the aesthesio- 

 meter, obtained by Weber on a normal adult subject, and by 

 Landois on an intelligent boy of 12 years old. 



Adult. Boy. 



Tip of tongue 1-1 .1-1 



Palmar surface of third phalanx . . . . . .2-2 



Eed part of lips 4-5 



Palmar surface of second phalanx 5 3-9 



Palmar side of first phalanx . . . . . .5 



Dorsal side of third phalanx ....... 6-8 4-5 



Tip of nose 6-8 4-5 



Ball of thumb 7 



Middle of palm . 8-9 



Middle of dorsum and edge of tongue 9 6-8 



Metacarpus of thumb 9 6-8 



Plantar surface of third phalanx of big toe . . . .11-3 6-8 



Dorsal surface of second phalanx . . . . . .11-3 9 



Cheek 11-3 9 



Eyelids 11-3 9 



Centre of hard palate 13-5 11-3 



Palmar side of lower third forearm 15-0 



Anterior part of zygomatic region . ..... 15-8 11-3 



Plantar side of metacarpus of big toe 15-8 



Dorsal surface of first phalanx 15-8 9 



Dorsal head of metacarpus . . . . . . .18 13-5 



Inner part of lips 2*0-3 13-5 



Posterior part of zygomatic region 22-6 20-3 



