86 BIOLOGICAL PHYSICS 



course of a large portion of the peripheral nerve fibres, 

 comprising the nerve trunks of a great proportion of the 

 systemic nervous system, and it may be certain com- 

 municating filaments of the sympathetic system, and being 

 thus so well defined and so widely distributed, we must 

 suppose that they possess functions and perform a duty, 

 or duties, static or dynamic, in the complicated economy 

 of the nervous system. We must, consequently, proceed 

 to assign a use, or function, to the " nodes of Ranvier," 

 and in doing so we must observe that a tube like the 

 containing sheath of the " white substance of Schwann," 

 and of the axis cylinder substance, must be subjected to 

 great strains from external pressure, as well as from the 

 disrupting influence of bulging from within due to 

 disturbances of the continuity of their contents, which, we 

 may take it, are usually in a semi-fluid state. We 

 therefore consider ourselves warranted in regarding these 

 structures, these " nodes of Ranvier," as circular supports 

 developed in, and around, the substance of the primitive 

 membrane, or containing wall, of the " white substance of 

 Schwann/' in the manner of strap and buckle arrangements 

 of their constituent material ; and that it is further 

 possible to recognise, as the agents in their production, 

 growth, and continuation, the c ' nerve corpuscles " or 

 " cells " distributed along the course of the same mem- 

 brane. 



If this strengthening or supporting function of these 

 " nodes " be granted it is no longer a matter of surprise or 

 wonder that a peripheral- or systemic-nerve- or trunk- is 

 such a resisting structure, and that the continuity of the 

 axis cylinders of its component fibres is so admirably 

 maintained and ensured. The " nodes of Ranvier " must 

 therefore rank as adaptations of texture to meet special 

 emergencies of the greatest importance. But it seems to 

 us that besides the function of support performed by the 

 " nodes of Ranvier " to the sheath of Schwann, they also 

 may be regarded as valves (Fig. 20) in the circulation of 

 the " white substance of Schwann," and axis cylinder 

 substance within their sheaths, allowing of the passage of 

 these substances towards the periphery of the nervous 

 system, but opposing a barrier to their regurgitation or 



