THE NERVE ELEMENTS. 



149 



the neurons in this instance do not always have a similar 

 size, but differ so far that one can be regarded as the 

 main stem of which the other is a branch. The impor- 

 tant idea involved in this conception is, that the portion 

 of the neuron appearing single and passing between the 

 cell-body and the point of branching, contains by virtue 

 of its origin two pathways for impulses, one going to the 

 cell-body and the other coming from it. If this be cor- 

 rect, it is but a step to the cells whose neurons have 



FIG. 23. Dineuric changing into mononeuric cells. From the 

 Gasserian ganglion of a developing guinea-pig. (Van 

 Gehuchten.) 



many branches, yet it must be admitted that but few 

 facts are available in support of this view, involving 

 as it does the notion that in the main stem the con- 

 tinuations of the branches are related to one another 

 like isolated wires in a cable. The current explana- 

 tion of the arrangement of the cell has been presented 

 by Cajal and Kolliker. It is based on the notion 

 that all the outgrowths of the cell are primitively 

 similar in function. Accordingly, both the dendrons 

 and the neurons are to be considered pathways for 

 impulses, and the chief difference between them physio- 

 logically is assumed to depend on the fact that while 

 the dendrons convey impulses towards the cell-body, 

 the neuron carries them away from it. 



