HuBER, SympatJietic Nervous System, yj 



giving off only a few branches {collateral branches) in its course, 

 and terminating in a complex of end branches, — the end-brush. 

 Such branches are described as axis-cylinder processes or neiir- 

 axes. The other kind of processes, not so essential, as many 

 cells do not possess them, are the protoplasmic branches or den- 

 drites. The dendrites may be said to be of two distinct types, — 

 in the one, belonging to cells of sensory ganglia, the single den- 

 drite present may also attain great length, become the axis- 

 cylinder of a nerve fiber, and also terminate in an end-brush ; 

 in the other type, the dendrite or the dendrites break up near 

 the cell body into secondary and tertiary branches and so on, 

 also ending free. To such nerve units, consisting of cell body 

 and nucleus, of neuraxis and its end-brush, and of dendrites, if 

 present, the term netiron has been applied by Waldeyer. Every 

 neuron therefore is a distinct anatomical unit, a distinct struc- 

 tural element, as much so as an epithelial cell, or any other 

 cell. This netiron-conception of the structure of the nervous 

 system is applicable to all its parts, to the brain and cord and 

 all peripheral ganglia ; and has been a most potent factor in the 

 development of our knowledge of the finer anatomy of the nerv- 

 ous system. 



Recent investigations have further shown that while a neu- 

 ron is a distinct anatomical unit, it is always found associated 

 with other neurons. Nowhere in the body of a vertebrate 

 does one find a neuron completely disconnected from other 

 neurons, or as Donaldson (8) has expressed it: "A group of 

 nerve cells completely disconnected from other nerve tissues of 

 the body, as muscle or glands are disconnected, would be with- 

 out physiological significance." This association of one neu- 

 ron with another is brought about by the close contiguity 

 always existing between the end-brush of the neuraxis ( or the 

 end-brush of one of its collateral branches ) of one neuron, and 

 the cell body or dendrite of one or several other neurons. Inves- 

 tigations with Golgi and methylen-blue methods have shown 

 that the neuraxis of one neuron may, with its end-brush, sur- 

 round the cell body of another neuron by the formation of what 

 is known as an end-basket; or the end ramifications of the neu- 



