THE ORGANS OF SPECIAL SENSE. 471 



probability perfectly identical, and the reason that one gives 

 rise to sensations of light, the other to those of sound, and 

 a third to perceptions of touch is not due to any difference 

 in these impulses, but is due to the centers in the brain in 

 which they end. Although such a thing is entirely impos- 

 sible in reality it is possible to imagine, and justly so, that 

 if the auditory nerve could be made to run to the visual 

 center in the brain, sound would be interpreted as light, 

 while if the optic nerve should end in the upper temporal 

 lobe, colors would be interpreted as sounds. 



A complete organ of special sense, then, is a special 

 nerve center in the brain and a special apparatus at the 

 distal end of a nerve connected with it. The phenomena 

 of the special sensations therefore naturally fall into two 

 kinds: the phenomena that take place in the end organs, 

 and those that take place in the brain. Our knowledge of 

 the processes which occur in the brain center is from a phy- 

 siological standpoint so meager that for evident reasons it is 

 here omitted altogether. Pure physiology concerns itself 

 now mainly with those nervous changes which occur at the 

 distal end of the nerve. We may speak of a complete sen- 

 sation consisting of two events; the first, a neurosis a 

 nervous impulse of some kind produced in a special way in 

 a special end organ and conveyed along a nerve to a special 

 center in the brain. The second event, the psychosis, a 

 conscious perception and interpretation of this nervous state 

 as a sensation. It is difficult here to avoid confusion in 

 the employment of the word tc sensation. " Frequently it 

 is used to include both the nervous changes and the psycho- 

 logical results which it calls forth. At other times the word 

 "sensation" is used to designate merely the psychological 

 result. The reader must himself judge carefully from the 

 context in which the word occurs what application is given 

 to the term. 



The neurosis is always the cause of the psychosis, unless 

 one should except certain forms of mental hallucination 

 which appear so real to the person as to be objectified. 



