CHAPTER XX 

 SENSE ORGANS IN GENERAL 



TPIE sense organs are the apparatus in which the periph- 

 eral sensory nerves end and which are stimulated by external 

 or internal influences. The sensory nerves take up the im- 

 pulse and carry it to the central nerve organ,. 



The sense organs are built for the reception of " ade- 

 quate " stimuli and are generally acted upon by these. 



The adequate stimuli for the eye are the ether vibrations of 

 certain length ; those for the ear are certain vibrations of air. 



The stimulation of the sensory nerves produces sensations 

 in the cells of the cerebral cortex to which they lead. 



The sensations may differ from each other in quality and 

 intensity. 



As differing in quality we regard, e.g., the different sensations 

 of colors, or sounds, or smell, etc. ; while the light and dark 

 sensations, or the loud and low sound sensations, are regarded as 

 differing in intensity. 



Law of tJie specific energy of the sensory nerves. The 

 quality of the sensation is constant for each sensory nerve 

 and is independent of the nature of the stimulus. 



For example, the stimulation of the optic nerve always causes 

 a sensation of light, whether the nerve be stimulated by the 

 adequate or by some other stimulus (mechanical, electrical). 



In what manner the specific energy of the sensory nerve 

 is determined is not fully known. We know no differences 

 in the structure or physiological stimulation processes in the 

 nerve elements (fibres and cells) which could determine this. 

 difference in the specific enefgy of the sensory nerves. 



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