ON NERVINE SECRETION 85 



stance, is said to be interrupted by the " nodes of Ranvier " 

 (Figs. 8, 20), but we contend that this is only apparent and 

 not real, and that the apparent interruption is due to the 

 compression, but not to the complete interruption, of its continuity 

 exercised by those nodes, and thus, moreover, is secured 

 the apparent raison d'etre of this insulating protecting 

 medium. The axis cylinder being necessarily for func- 

 tional purposes, continuous from source to termination in 

 its fully formed or normal condition within each neuron, 

 and depending for its integrity on the completeness of its 

 surroundings and insulating structures, we feel ourselves 

 warranted in inferring that the " white substance of 

 Schwann," with its containing sheath or neurilemma, is also 



FlG. 20. A SMALL BUNDLE OF NERVE FIBRES FROM THE SYMPATHETIC 



NERVE. (Key and Retzius.) 



The bundle is composed of pale nerve-fibres, with the exception of the fibre m, m, 

 which is enclosed here and there by a thin medullary sheath ; n, n, nuclei of 

 pale fibres. 



continuous,' although the apparent interruptions in its 

 course caused by the occurrence of the " nodes of 

 Ranvier" seem to militate against that view. Thus, 

 circulation of a somewhat limited extent is possible here, 

 and, we think, required to maintain the continuity, and 

 hence the vitality, of this viscous, but yet fluid, substance, 

 and we, therefore, regard it as adding one more to the far 

 from exhausted series of human corporeal circulations. 



Our reference to the "nodes of Ranvier" and our 

 expression of dissent from the received opinion regarding 

 their complete interruption of the continuity of the 

 medullary or " white substance of Schwann," necessitate 

 we think a further reference and, if possible, a fuller 

 explanation of the questions involved. The " nodes 

 of Ranvier" are histologically well-defined structures, 

 occurring at certain, but varying, intervals, along the 



