178 



THE HUMAN BODY 



tain skin areas; and that since painful skin stimulation is much 

 more common than internal pains, the brain interprets all im- 

 pulses reaching it over a restricted nerve-path as coming from 



the particular skin area whose nerve- 

 path forms part of the whole nerve- 

 path in question. 



Touch, or the Pressure Sense. 

 Through touch proper we recognize 

 pressure or traction exerted on the 

 skin, and the force of the pressure; 

 the softness or hardness, roughness or 

 smoothness, of the body producing 

 it ; and the form of this, when not too 

 large to be felt all over. When to 

 learn the form of an object we move 

 the hand over it, muscular sensations 

 are combined with proper tactile, and 

 such a combination of the two sen- 

 sations is frequent; moreover, we 

 rarely touch anything without at the 

 same time getting temperature sensations; therefore pure tactile 

 feelings are rare. 



From an evolution point of view, touch is probably the first 

 distinctly differentiated sensation, and this primary position 

 it still largely holds in our mental life; we mainly think of the 

 things about us as objects which would give us certain tactile 

 sensations if we were in contact with them. Though the eye 

 tells us much quicker, and at a greater range, what are the shapes 

 of objects and whether they are smooth, rough, and so on, our 

 real conceptions of round and square and rough bodies are de- 

 rived through touch, and we largely translate unconsciously the 

 teachings of the eye into mental terms of the tactile sense. 



The delicacy of the pressure sense varies on different parts 

 of the skin; it is greatest on the forehead, temples, and back of 

 the forearm, where a weight of 2 milligr. (0.03 grain) pressing on 

 an area of 9 sq. millim. (0.0139 sq. inch) can be felt. On the front 

 of the forearm 3 milligr. (0.036 grain) can be similarly felt, and 

 on the front of the forefinger 5 to 15 milligr. (0.07-0.23 grain) . 

 In order that the sense of touch may be excited neighboring 



FIG. 67. A Pacinian corpus- 

 cle, magnified. 



