CHAPTER XVIII 



PAIN AND PLEASURE 



FEW problems in neurology are more difficult and involved 

 than those centering about the nerves of painful sensibility. 

 This question is intimately related with the disagreeable and 

 pleasurable feelings and with the affective and emotional life as a 

 whole. Nearly all sensations, whether of the somatic or visceral 

 series, appear to have an agreeable or disagreeable quality 

 (quale). There is difference of opinion as to whether any sensa- 

 tion is wholly indifferent in this respect. There are, however, 

 two factors in this situation which have not always been dis- 

 tinguished and whose introspective analysis is very difficult. 

 In the first place, many sensations are as such painful or pleasur- 

 able, and in the second place the related apperceptions, ideas, 

 etc., may have an agreeable or disagreeable feeling tone. The 

 intimate relation of these two factors in consciousness probably 

 grows out of a similarity in the type of physiological process 

 involved in their neurological mechanisms, and this, in turn, 

 may rest on the fact that the two mechanisms in question have 

 had a common evolutionary origin. 



The stimulation of some of the sense organs results in the so- 

 called sensation of pain with no other quality recognizable; 

 this is true of the cornea, of the tooth pulps, of the tympanic 

 membrane, and of the "pain spots" of the outer skin. This fact 

 would suggest that there is a special system of neurons (or at 

 least of receptors, see p. 85) for pain as for the other senses. 

 But, on the other hand, the supernormal stimulation of most 

 other sense organs may result in a very similar type of pain, 

 though in this case the painful quality is accompanied by the 

 normal sensory quality of the organ in question unless the stimu- 

 lation is excessively strong. From this it would appear that 

 most sensory nerves may upon occasion function as pain nerves. 

 In other cases normal stimulation of a sense organ may result in 



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