42 PHYSIOLOGY CHAP. 



According to Sherrington, cerebral cortical lesions in man 

 disturb tactile localisation far more than any other form <>!' 

 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. 



(6) The same occurs if, in estimating the limiual 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 witli indifferent fluids increases tactile 

 discrimination, i.e. the discrimination is sharpened. 



() 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. 



