THE FINER STRUCTURE OF THE NERVOUS SYSTEM 



561 



fibers from without. Accepting this view, this pericellular network would 

 be analogous to the extracellular fibrillary reticulum in the neuropile of 

 the invertebrates. In view of the fact that it is not confined alone to the 

 surface of the cell, but spreads out in three dimensions through the entire 

 gray matter of certain parts of the nervous system, this network may be looked 

 upon as constituting a new kind of nerve matter, probably corresponding to 

 the extracellular " gray " whose existence was postulated by Nissl. Nissl's 

 inference was based on the ground that even the great number of nerve cells, 

 dendritic and axis-cylinder processes, neuroglia fibers and cells, and blood 

 vessels taken collectively, especially in certain parts of the cerebral cortex 

 but also in other places, fall far short of the bulk necessary to fill the entire 

 space. 



What the genetic relationship is that exists between the reticulum of the 

 invertebrate ganglion or the Golgi network of the vertebrate nerve tissue 

 if indeed it be a nervous structure and the nerve cells is still quite unknown. 

 Even if the pericellular network takes its origin from the nerve cells and is 

 therefore to be regarded as a de- 

 rivative of such a structure, the 

 classical definition of the neuron 

 theory makes no provision or quali- 

 fication for such an additional ele- 

 ment. Moreover, Bethe and others 

 have made observations which pur- 

 port to show that the nerve fibers 

 are not produced as outgrowths of 

 the nerve cells but are laid down 

 separately by other cells. If this 

 be true, the neuron theory cannot 

 be maintained in any form. But 

 since much remains yet to be 

 cleared up in regard to this ques- 

 tion, and since different facts of ex- 

 perimental physiology which Bethe 

 has advanced in support of his 

 view (cf. page 575) really admit 

 of another theoretical construction, 

 the objection last urged against the 

 neuron theory can scarcely yet be 

 accepted as conclusive. 



FIG. 253. Golgi network about a , cell of the 

 nucleus dentatus of the dog, after Bethe. 



At present we may view the 

 structure of the nervous system 

 somewhat as follows: The nerve 

 cells give off several processes, one 



or more of which become the axis cylinders of nerve fibers. These consist of 

 fine fibrils which pursue a separate and unconnected course in the nerve fiber, 

 oftentimes penetrate the nerve cell and there in the invertebrates, but not in 

 the vertebrates form a real network. These fibrils anastomose freely outside 

 the nerve cells, and also within the cells in the invertebrates, and thus consti- 

 tute a possible path for the transmission of stimuli from one cell to the other. 



