THE SPECIAL SENSES 267 



upon the sensory fibres of the spinal nerve. The face, how- 

 ever, is supplied by the sensory cranial nerves. The sympa- 

 thetic system has a low grade of feeling in health, but disease 

 in the parts served by it arouses an intense degree of pain. 



8. The Sensation of Pain. What then is pain? Is it iden- 

 tical with ordinary sensibility ? There seems to be some 

 necessary connection between the two feelings, for they take 

 place through the same channels, and they are alike intense in 

 the same situations. But sensibility habitually contributes to 

 our sources of pleasure the very opposite of pain ; hence, 

 these feelings cannot be identical. 



9. Pain must, therefore, "be a modification of the general 

 sensibility which follows an excessive degree of excitement of 

 the nerves, there being a natural limit to the amount of stimu- 

 lation which they will sustain. So long as this limit is observed, 

 the part excited may be said to be simply sensitive ; but when 

 it is exceeded, the impression becomes painful. This difference 

 between sensibility and pain is well shown by the effects of 

 sunlight upon the eye. The indirect illumination of the sun 

 arouses only the former feeling, and is indispensable to our 

 comfort and existence, while the direct ray received into the 

 eye occasions great pain. 



10. The Uses of Pain. The dread of pain is a valuable 

 monitor to the body. It puts us on our guard in the presence 

 of danger, teaches moderation in the use of our powers, indi- 

 cates the approach of disease, and calls attention to it when 

 present. The word disease, in fact, according to its original 

 use, had reference simply to the pain, or want of ease, which 

 commonly attends disordered health. When we observe the 

 serious mishaps which occur when sensibility and pain are 

 absent, we cannot fail to appreciate its value. For example, a 

 paralytic, in taking a foot-bath, forgets to test its temperature, 

 and putting his limbs into water while it is too hot, is severely 

 scalded without knowing it. 



8. Connection between pain and sensibility ? 



9. Explain the difference between pain and sensibility. 



10. Dread of pain ? How may its value be appreciated ? Example ? 



