SECTION III. 

 THE SPECIAL SENSES. 



CHAPTER XIV. 



CLASSIFICATION OF THE SENSES AND GENERAL 

 STATEMENTS. 



Under the general term sense organ we may include not only 

 the peripheral organ on which the stimulus acts, but also the sensory 

 path through which the impulses are conveyed to the central 

 nervous system and the cortical center b}' means of which the 

 reaction in consciousness is mediated. 



Classification of the Senses. — In general, we attempt to 

 distinguish the various sense organs by the differences in their 

 end reaction in consciousness. Each sense organ gives a different 

 kind of response, the nature and distinctive features of which 

 are recognized subjectively. The conscious sensations are said 

 to differ in quality or modality. The quahtative difference in 

 some cases is very distinct, —the difference between sensations of 

 sound and of vision, for instance, — and on this subjective difference 

 we base our efforts to give specific names to the sense organs con- 

 cerned. This means of classification is not, however, applicable 

 in all cases. ^Yhl\e many of our sensations are so distinct in quality 

 that we can recognize them and name them without difficulty, 

 others are of a more obscure character. In addition to our sensa- 

 tions of vision, hearing, smell, taste, pressure, temperature, and 

 pain, there are doubtless many other sensations whose conscious 

 reaction is less distinct in quality and for which our subjective 

 means of recognition and classification are less satisfactory or 

 entirely inadequate. Such, for instance, are the sensations from 

 the muscles, from the semicircular canals and the vestibular sacs 

 of the ear, and from many of the visceral organs. For the recogni- 

 tion and classification of these senses and sense organs it is neces- 

 sary^ to fall back upon the methods of anatomical and physiological 

 analysis, methods which in many respects are uncertain. So also 

 within the limits of any sensation of a given quality or modality, 

 we distinguish certain subqualities. In vision we have many dif- 



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