CHAPTER XXXIV 



THE ORGANS OF SENSE 



We become aware of objects in the outer world through 

 our organs of sense; these when stimulated set up im- 

 pulses which are conveyed by sensory nerve fibers to the 

 brain and arouse sensations of various kinds according 

 to the kind of sense organ affected. Each sensation that 



we feel has its own peculiar 

 sense organ which is especi- 

 ally sensitive to a particular 

 activity in the outer world. 

 Contact for instance stimu- 

 lates the organs of touch, 

 sound waves the organs of 

 hearing, and light affects the 

 organs of vision. Were it 

 possible to destroy all of our 

 sense organs or the nerves 

 which lead from them to the 



FIG. 216. Tongue, i, circum- 

 vallate papillae; 2, circumvallate 

 papilla, large; 3, toad-stool (fungi- centra l nervOUS System, the 



outer world would make no 



form) papillae; 4, threadform (fili- 

 form) papillae. 



impression on us. 



Some of our sense organs are distributed over most of 

 the surface of the body, while others are limited to well- 

 defined areas. We may feel sensations of touch over most 

 of the skin and in various internal organs, but there are 

 some areas such as the tip of the tongue and the ends of 

 the fingers where tactile sensibility is especially acute. 

 Heat and cold are likewise felt over most of the surface of 



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