HISTOGENESIS AND PHYSIOLOGY OF THE 

 NERVOUS ELEMENTS.! 



C. L. Herrick. 



Structurally the nervous system may be said to con- 

 sist of a single remarkably constant element — the neuron. 

 The neuron is fundamentally a cell with a certain amount 

 of unstable protoplasm which may suddenly be excited to 

 an explosive form of decomposition which propagates itself 

 at the comparatively slow rate of 33 yards a second along 

 the nerve fibres which are immediate outgrowths of the 

 cells. Every such. cell has one or more tube-like prolonga- 

 tions of its protoplasm forming the nerve fibre or ' ' axis- 

 cylinder" and also a number of branching root-like projec- 

 tions, or "protoplasmic processes." The latter terminate 

 in minute fibrils which serve to connect the cell with its 

 neighbors and other nerve paths. Although once sup- 

 posed to serve the nutrition of the cell, it seems quite cer- 

 tain that these minute fibres transmit nervous stimuli to 

 adjacent organs. 



It is interesting to recall that, in the early stages of 

 development, all nervous structures are derived from 

 special portions of the surface of the embryo and that all 

 the neurons, whether destined to form the retina or olfac- 

 tory epithelium or to become a part of the mechanism of 

 voluntary processes in the hemispheres, arise as products 

 of cell-division from this primitive nervous epithelium. By 

 a process which may be aptly compared to the formation 



IReprinted from The Denison Quarterly, with the consent of 

 the Editor. 



The type here used is that which will be employed in Vol. III. 



