THE SYSTEMIC NERVE CELL 319 



and being plastic or fluid enough to circulate, they are con- 

 stantly liable to suffer from stases and disturbances of their 

 continuity within the lumina of the tubes or containing 

 walls along which they are moving or circulating, from " a 

 thousand and one " causes. We would expect, therefore, 

 to find that their onward and outward movement is safe- 

 guarded and secured against the possibility of destructive 

 regurgitation, and we think we have discerned the existence 

 of the required means in the cellular and fibral arrange- 

 ments and re-arrangements within the brain cord and nerves, 

 the last mentioned and the nerves being specially protected 

 by the introduction and continuous reproduction, it may 

 be, of the histological textures known as the " nodes of 

 Ranvier," which have already been described, and which, 

 we claim, allow of an efferent, but prevent an afferent 

 movement of the intra-neuro-fibral contents. 



The nutrition of the textures in question, viz. the 

 medullary and axis cylinder, with their enclosing or 

 containing walls, may be accepted as taking place, from the 

 matrix of the neuroglia, by the exercise of the inherent 

 selective and assimilative, or vital, powers, or properties of 

 the cell dendrons, determined and sustained by their con- 

 tained nucleoli, the presence of which latter is to be 

 regarded as essential to nerve cell existence. 



We are warranted here, we think, in concluding that 

 nowhere does communication exist between the nutritive 

 materials, directly or immediately, which pass from the 

 haemal to the neural structures, save by the intervention 

 or carrying agency, so to speak, of the neuroglial textures 

 nutrition of the neurons being universally due to, or 

 effected by, the selective influence exercised on the passing 

 blood streams by the neuroglial texture, through which the 

 required pabulum is supplied to the widely deployed and 

 constantly foraging dendrons of the waiting and hungry 

 cells. 



Thus we may regard the systemic nervous system as a 

 system within a system, or rather within a system of sys- 

 tems, and we may look upon these systems as being only 

 " the means to the end " of supporting and ministering to 

 the wants of a contained central material organism, capable 

 of being energised and wrought upon by an immaterial 



