Section 4. 

 The Cutaneous and Internal Sensations. 



The sensations imparted from the surface of the body to the 

 animal are not of one character only : touch is different from 

 heat, cold is something apart from pain. These four sensa- 

 tions of pressure or touch, heat, cold, and pain, make up the com- 

 plex, combined or uncombined, which composes the cutaneous 

 senses. It is easy to realise the remarkably sensitive nature of 

 the entire surface of the body. There is no part, excepting the 

 horn of the feet or head, which does not give evidence of pain 

 on being cut ; there is no part, including the feet and horns, which 

 is unconscious of touch or pressure. This sensory envelope is 

 in the main protective, but it serves many other functions ; some 

 of these we have already studied under Respiration, Secretion, and 

 Animal Heat ; some have been referred to under the head of Muscle 

 Tonus, on which much more remains to be said. But besides 

 these, there are afferent impulses proceeding from the skin which 

 indicate to an animal the position of its limbs, which direct its 

 muscular efforts, enable it to judge of weight and resistance and, 

 in conjunction with afferent impulses from muscles, initiate the 

 changes which lead up to a muscular contraction. With none 

 of these are we at present concerned, but only with those afferent 

 impulses of common sensibility and pain proceeding from the 

 skin to the central sense-organs, where their nature and character 

 can alone be realised and distinguished, though the sensation is 

 referred to the stimulated surface, and not felt in the brain. 



In the matter of sensibility there is a great contrast between 

 the surface of the skin and all that lies beneath it. Muscles, 

 bones, and tendons^ exhibit no ordinary sensibility ; the same 

 applies to the viscera, heart and lungs, liver, kidneys, and 

 intestinal canal, which are partly or wholly without sensation. 

 Under normal conditions the above structures, even when 

 aroused by disease, are still devoid of touch, heat, and cold, 

 though pain may be felt acutely. 



Experiments made by Head and Rivers have shown that 

 there are two sets of sensory skin-fibres-^-a deep and super- 

 ficial. The former convey sensations of pain, and of marked 

 heat and cold ; the latter convey sensations of touch, 

 and small differences of heat and cold. Touch sensations 

 are divided into those of tactile localisation and tactile dis- 

 crimination ; these are conveyed by separate nerve-fibres — in 



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