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NERVE 101 



Tn fact pain is purely a relative term, and conditions 

 which in one animal will cause pain will not cause it in 

 another, while stimuli which will produce what are called 

 painful sensations when the nervous system is debilitated 

 may give rise to sensations not considered as painful when 

 the nervous system is normal. 



All pain, since it means a change in consciousness, 

 is metaphysical. There is no such tiling as " physical pain." 

 The fatigue and the other sequences to any kind of pain are 

 frequently cited as proofs of the influence of the mind on 

 the body. But we have no right to assume that they are 

 caused by the " pain " rather than by the physical disturb- 

 ances in the nervous system of which the pain is an 

 accompaniment. 



Separate nerve fibres appear to carry pain-producing 

 impulses up the spinal cord, and in some diseases the sense 

 of touch may be lost without loss of the sense of pain, and 

 vice versa (p. 112). 



2. Reactions to Contact. 

 The Tactile Sense. 



The tactile sense may best be studied under three 

 heads : — 



1. The Power of Distinguishing Differences of Pressure. — 

 Variations of pressure in time and space are alone distin- 

 guished. We live under an atmospheric pressure of 760 

 mm. of mercury, but this gives rise to no sensation. Any 

 sudden increase or diminution of pressure, however, leads to 

 a marked change of sensation, but a slow change causes a 

 lesser modification of consciousness. When a finger is im- 

 mersed in mercury, the sensation of pressure is felt as a 

 ring at the surface of the mercury, where the greater pres- 

 sure of the mercury joins the lesser pressure of the air 

 (Practical Physiology). 



The acuteness of the pressure sense varies in different 

 parts of the body, being greatest where the nerve terminations 

 are most abundant, as in the lips of the horse. 



The acuteness of the sense is influenced by the condition 



