2l8 THE HUMAN BODY. 



be the seat of impressions which may be referred to the 

 general sensibility, and which are for the most part painful; 

 impressions on the sense of touch are only produced in 

 certain tissues specially endowed with this sense. General 

 and tactile sensibility are independent of each other, and 

 they are not developed proportionally; as, for instance, the 

 palmar surface of the ringers is endowed with an exquisite 

 sense of feeling, but it is almost insensible to a blow which 

 would be very painful to the cheek, in which this sense is 

 much less developed. 



Organ of touch. Touch has its seat in the skin throughout 

 its whole extent, and in some of the mucous membranes. It 

 is by the nervous papillae containing the tactile corpuscles 

 that the impression is perceived, and the tactile sensibility of 

 any region is in proportion to the number of nervous papillae 

 existing in it. 



We receive three distinct impressions at a time by the 

 sense of touch that of contact from a foreign body, that of 

 the pressure which it exercises on the skin, and that of its 

 relative temperature. 



The sensation of contact is not equally distinct and precise 

 in all parts of the body, and the reason of this we will 

 endeavour to explain. If we apply simultaneously the two 

 points of a compass to the skin, they must be more or less 

 separated according to the region experimented on, in order 

 that their contact may cause one or two distinct sensations, 

 and we may in this way measure the delicacy of the sense at 

 any given point on the skin. It is evident that the less 

 sensitive the skin is, the more widely we must separate the 

 points of the compass to produce a double sensation. 

 E. Weber after many experiments classes the regions in the 

 order of their sensibility as follows : The tip of the tongue 

 gives a double sensation when the feet of the compass are 

 separated about half a line ; the palmar surface of the ends 

 of the fingers, one line; the red surface of the lips and the 

 surface of the second joint of the fingers, two lines; the end 

 of the nose and the palm of the hand near the fingers, three 

 lines; the back and edges of the tongue at about an inch 

 from the tip, and the skin of the lips, four lines; the palm 



