THE STORY OF NINETEENTH-CENTURY SCIENCE 



A most interesting body it proved, this. nerve cell, or 

 ganglion cell, as it came to be called. It was seen to be 

 exceedingly minute in size, requiring high powers of the 

 microscope to make it visible. It exists in almost infi- 

 nite numbers, not, however, scattered at random through 

 the brain and spinal cord. On the contrary, it is confined 

 to those portions of the central nervous masses which to 

 the naked eye appear gray in color, being altogether 

 wanting in the white substance which makes up the chief 

 mass of the brain. Even in the gray matter, though 

 sometimes thickly distributed, the ganglion cells are 

 never in actual contact one with another ; they always 

 lie embedded in intercellular tissues, which came to be 

 known, following Virchow, as the neuroglia. 



Each ganglion cell was seen to be irregular in con- 

 tour, and to have jutting out from it two sets of mi- 

 nute fibres, one set relatively short, indefinitely numer- 

 ous, and branching in every direction ; the other set 

 limited in number, sometimes even single, and starting 

 out directly from the cell as if bent on a longer journey. 

 The numerous filaments came to be known as proto- 

 plasmic processes; the other fibre was named, after its 

 discoverer, the axis cylinder of Deiters. It was a natural 

 inference, though not clearly demonstrable in the sec- 

 tions, that these filamentous processes are the connect- 

 ing links between the different nerve cells, and also the 

 channels of communication between nerve cells and the 

 periphery of the body. The white substance of brain 

 and cord, apparently, is made up of such connecting 

 fibres, thus bringing the different ganglion cells every- 

 where into communication one with another. 



In the attempt to trace the connecting nerve tracts 

 through this white substance by either macroscopical or 



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