Touch. 429 



The scnsibilit}' of the skin in different parts varies greatly, and the 

 number of the tactile papillae is much greater in some parts than others. 

 Another peculiar circumstance is, that although every particle of the 

 surface of the skin can convey to the brain the stimulation of touch, it 

 does not convey an impression of its exact locality. If a pair of divid- 

 ers with blunted points, spread apart to a distance of say half an inch, 

 be applied to certain parts of the skin so that both points touch the skin 

 at the same time, the person touched will feel the two as only one. The 

 entire skin may be divided into circles of various sizes within which two 

 or more simultaneous stimulations of the skin will be felt as only one. 

 The body has been gauged all over with dividers and the sizes of these 

 circles determined They are smallest in the tip of the tongue and the 

 tips of the fingers, the parts most used in touching. 



The following is a table of the smallest distances apart of the legs of 

 the dividers at which they were felt to be distinct from one another. 

 The figures are lines, twelfths of an inch : 



Point of tongue Gums 9 



Inner face, middle finger 1 Lower part of forehead 10 



" " index " 2 Neck below the jaw 15 



Lips, red part 2 Skin over lower back bone ... 18 



Palm of hand 3 Top of foot 18 



Tip of nose 3 Skin over breast bone 20 



Edge and top of tongue 4 Middle of back 30 



Cheek 5 " " arm 30 



End of big toe 5 " " thigh. .30 



Back of hand 8 



Thus it appears that the parts most active in touching are the most 

 sensitive ; which, of course, was to be expected. The parts least sensi- 

 tive are those least exposed to touch stimulations ; and it is curious to 

 observe the increase of sensitiveness as the chief centers of stimulation 

 are approached. If the points of the dividers are separated to 6 or 8 

 lines, and placed on the cheek near the ear, they will be recognized as 

 being barely distinct. If they are then drawn slowly toward the lips, 

 they will give the impression that they are getting further apart as they 

 advance ; for the reason that they are moving from larger to smaller 

 circles, that is, into a more sensitive tract. The same sensation is ex- 

 perienced when the points are placed across the fore-arm and drawn 

 down the arm and hand to the tips of the fingers. In the middle of the 

 back the points must be two and a half inches apart before they are 

 each able to give a sensation independent of the other. We shall see 

 further on that all parts of the body are represented in the brain. One 

 portion of the brain receives the stimulations of sight, another of hear- 

 ing, a third of touch, &c. , and every cell of the brain is connected by 

 a nerve fibre with its own definite part of the body. But it does not 

 follow that every cell in the body has its corresponding brain cell ; 



