70 S. AVALTER RANSON 



to have shrunken. Imbedded in the light yellow endoneurium 

 which separates the individual medullated fibers are black dots, 

 which, unless the preparation is very thin, can be seen to be the 

 cut ends of small black fibers. They vary in size. Some are as 

 large as the axons of the smallest medullated fibers, others much 

 smaller. Their grouping is quite characteristic; running for the 

 most part in bundles, they appear on cross section as clusters of 

 dots. Isolated fibers are however not uncommon. The non- 

 medullated fibers are not uniformly distributed throughout the 

 nerve, in some fields only a few scattered groups can be seen; 

 while in others they greatly outnumber the medullated axons. 



Oblique sections give the most convincing demonstration of 

 these fibers. In a good Cajal preparation the background is so 

 faintly stained that sections 20fx thick are not at all obscure. 

 In such a preparation it is possible, beginning with the lower 

 surface of the section in focus, to see the sharply defined ends of 

 the cut fibers and by raising the focus gradually follow these 

 same fibers obliquely upward through the section in a somewhat 

 undulating course between the medullated fibers, and on reach- 

 ing the upper surface of the section see them terminate again in 

 sharply defined rounded dots. This oblique course has been 

 verj^ difficult to reproduce in a drawing but an attempt has been 

 made to illustrate it in fig. 2. In longitudinal sections these 

 fibers can be followed for a considerable distance. They have not 

 been seen to branch, but no special search has been made for 

 branching fibers. 



About some of these axons a faint halo can be seen, a ring so 

 delicate that it can be recognized only with the highest magnifi- 

 cation. Its significance has not been determined, but two possi- 

 ble explanations must be considered. The rings maj?- be produced 

 by the shrinking of the axon or there may be a definite sheath 

 (aside from the neurilemma) surrounding non-medullated fibers. 

 This view has been upheld by ShiefTerdecker and Tucket t. 

 According to the latter these sheaths are destitute of myelin, 

 while according to the former they contain a faint trace of that 

 substance. This opens up an interesting question concerning 

 the structure of non-medullated fibers which will require careful 



