EXTRACT XXX. B. 



ON THE NEURON, OR NERVE UNIT. 



THE study of the neuron may be pursued, along the 

 individual line, so as to afford a clearer view of the united, 

 or general, lines, when we come to take up the subject of 

 the neurons, in their co-relations to each other, and to 

 the, so-called, non-nervous structures of the body. The 

 neuron, as we have already said, is composed of a cell, 

 with its contained, nucleus, and nucleolus, having attached 

 to its outer, or containing, wall, a series of processes, or 

 projections, called dendrons, or dendrites, together with 

 one, or more, processes of a special structure, called 

 axons, which represent the path, or paths, along which 

 nerve impulses, sensory, and motor, pass, into, or out of, 

 the cell contents. Covering the cell protoplasm, the 

 nuclear, and nucleolar, bodies, is a series of neuro- 

 keratinous containing walls, of a very attenuated, but 

 resisting, character, which, respectively, support, and 

 separate, them, and which, with the probable exception of 

 the nucleolar, are continued along the axons, and, it may 

 be, to some extent, the dendrons. In the case of these 

 latter, however, it may be premised, that protoplasmic 

 separation, gives place to blending, or, at any rate, that 

 the contained protoplasm has not begun to be, separated 

 by, or insinuated between, containing walls, in quantity at 

 all proportionate to that, which is regularly passed along 

 the axonal processes of the nerve fibres, but yet in sufficient 

 quantity, to permit of the collateral axonal or dendritic, 

 communication of nervine molecular changes, between 

 associated neurons, or groups of neurons, contiguity, if 



