SEC. 2. THE GENERAL FEATURES OF CUTANEOUS 



SENSATIONS. 



876. The sensations which we experience by means of the 

 skin and cutaneous nerves appear, in the first instance, to be 

 of at least three kinds. In the first place, all bodies, whatever 

 their chemical or physical nature, be they gaseous, liquid or solid, 

 when brought into contact with the skin, when made to exert 

 mechanical pressure on the skin, produce sensations of a certain 

 kind ; these sensations, whose characters depend mainly on the 

 amount of pressure exerted and on the region and area of the skin 

 pressed upon, may be conveniently spoken of as tactile sensations 

 or sensations of touch proper. In the second place, when either by 

 actual contact with, or by the mere proximity of hot or cold 

 bodies, of whatever nature, the temperature of an area of the skin 

 is changed with sufficient rapidity, we experience sensations of a 

 kind different from the tactile sensations just mentioned; these 

 we may speak of as sensations of temperature, sensations of heat 

 and cold. In the third place, when too violent a pressure is 

 exerted on the skin, or when the changes of temperature are 

 excessive, or when certain changes giving rise neither to tactile 

 nor to temperature sensations are produced, or take place in the 

 skin, we experience sensations which we call sensations of pain. 

 This third kind of sensation stands, in many respects, apart from 

 the other two, and it will be convenient to study sensations of 

 pain by themselves. Sensations of touch proper and of heat and 

 cold are much more akin and may be treated of together. 



Tactile Sensations or Sensations of Pressure. 



877. Many of the characters of tactile sensations are of 

 the same order as those of visual sensations, which we studied 

 somewhat fully, and indeed similar characters may ba more or less 

 distinctly recognized in all sensations. The amount, that is to 

 say the intensity of the sensation, varies with the amount of the 

 stimulus, with the amount of pressure brought to bear on a given 



