CHAPTER VI. 

 ON CUTANEOUS AND SOME OTHER SENSATIONS. 



SEC. 1. THE GENERAL FEATURES OF CUTANEOUS 



SENSATIONS. 



644. 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 ex- 

 perience sensations of a kind different from the tactile sensations 

 just mentioned; these we may speak of as sensations of tem- 

 perature, 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 temperate 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. Sen- 

 sations of touch proper and of heat and cold are much more 

 akin and may be treated of together. 



Tactile Sensations or Sensations of Pressure. 



645. 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 be more or 



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