ON THE NEUROGLIA 291 



to exercise, we cannot help thinking, a preservative 

 influence, in virtue, we may presume, mainly of its 

 chloride of sodium, acting on the faintly vital constitu- 

 tion, and non-, or slightly-, organised, neuroglial 

 substance. In this process is perpetuated, the operation 

 of the principle of circulation, or the onward flow of 

 living matter, in its progress, from the less organised, 

 to the more organised, condition, and is displayed what, 

 without exaggeration, may be denominated, a second 

 digestion, and assimilation, the first consisting of alimen- 

 tary, and the second of neuroglial, and neuronal, 

 phenomena, and each affording the starting-point for 

 new organic arrangements of matter, and the formation 

 of new structural, and organic, elements the earlier, 

 or alimentary, digestion, furnishing the nutritive pabulum 

 for the growth, and sustenance, of the sympathetic, or 

 non-systemic, nervous elements, of the bodily textures, 

 while the latter, or neuronal, digestion, supplies the more 

 elaborated, and highly potential, elements, for the growth, 

 and sustenance, of that truly wonderful compound of 

 materio-dynamic organisms constituting, what is known as, 

 the brain (Figs. 120, 121), and nervous system, wherein 

 dwells, and works, for good, or for evil, the presiding 

 mind, and immaterial essence, of man. 



In this process of secondary, or neuronal, digestion, 

 the nerve cells, by their dendrons, take up, and assimilate, 

 what is required for their own individual support, as well 

 as what is required for the maintenance of their contained 

 nuclei, and nucleoli, and pass it out, or excrete it, as 

 neural protoplasm, along the lumina of the cavities, tubes, 

 or inter-spaces, within the containing walls, or neurokera- 

 tinous sheaths, " of the white substance of Schwann," and 

 the axis cylinders, of their axons, respectively. In our 

 opinion, we are entitled to regard this, as a process of 

 growth, or circulation, along the channels, or spaces, 

 enclosed by the sheaths, respectively, of the medullary, 

 and axis cylinder, substances, which ends in organised 

 exudation, at the terminal extremities, or peripheral arbori- 

 sations, of the various nerve fibres, sensory, and motor. 



Whether the rate of progress of this growth, or circu- 

 lation, is equal, or approximately identical, in the two 



