THE NEURON 49 



cell bodies from which these fibers arise show structural changes. 

 The most important change is a solution of the chromophilic 

 substance or Nissl bodies so that they no longer appear in a 

 stained preparation (Fig. 13). This is termed chromatolysis, 

 and often enables the neurologist to determine exactly which 

 cells in the central nervous system give rise to a particular 

 bundle of fibers (for examples see pp. 136 and 284). 



The neuron doctrine may be said to date from the publica- 

 tion of important papers by Golgi, of Pavia, in 1882 to 1885 

 (though his now famous method was published in 1873, and 

 many of Golgi's theoretical conclusions have been greatly 

 modified). The name Neuron (in English often spelled 

 "neurone") was first applied by Waldeyer in 1891 in connection 

 with a clear enunciation of the recently demonstrated facts upon 

 which the concept is based. The discovery of William His 

 that the nervous system is made up of cellular units which are 

 embryologically distinct, and the further demonstration by 

 others that these cellular elements retain some measure of ana- 

 tomical and physiological individuality (the exact degree of 

 anatomical separation is still in controversy some say it is com- 

 plete) up to adult life revolutionized neurology, and this doctrine 

 has profoundly influenced all subsequent neurological work. The 

 history of this movement we cannot here go into (see the excel- 

 lent summaries in Barker's Nervous System and the article by 

 Adolf Meyer cited at the end of this chapter). The present 

 status of the neuron doctrine has been summarized by Heiden- 

 hain (1911, p. 711) in the following six propositions: 



1. The neuron of the adult animal body is an anatomical unit; 

 it corresponds morphologically to one cell. 



2. The neuron is, accordingly, also a genetic unit, for it is 

 differentiated from a single embryonic cell. 



3. Nervous substance is composed of the contained neurons; 

 within the nervous system there are no elements other than 

 neurons which participate in nervous functions. 



4. The neurons remain anatomically separate; they are merely 

 in contact with each other, that is, there are no connections 

 between them which are characterized as conditions of conti- 

 nuity or fusion of their substance. 



5. The neuron is a trophic unit. This means that the injury 



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