180 THE SPECIAL SENSES. 



sensations, as they are called, which depend upon the con- 

 dition of the internal organs, such as appetite, hunger, 

 thirst, the sense of satisfaction after taking food, dizziness 

 when looking down from some lofty position, lassitude, 

 drowsiness, fatigue, and other feelings of comfort or dis- 

 comfort. General sensibility, whether of the internal or 

 external organs of the body, chiefly depends upon the 

 sensory fibres of the spinal nerve. The face, however, is 

 supplied by the sensory cranial nerves. The sympathetic 

 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 9 Is 

 it identical 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 

 stimulation which they will sustain. So long as this limit 

 is observed, the part excited may be said to be simply sen- 

 sitive; 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 valu- 

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

 presence of danger; teaches moderation in the use of our 



8. Connection between pain and sensibility? 



9. Explain the difference between pain and sensibility. 



1O. Dread of pain * How may its value be appreciated ? Example. 



