76 ELBERT CLARK 



finden." This is a constant finding in fibers of the cord unless 

 special precautions are taken to produce marked inflammation 

 of the affected area, such as by infection. Then the degenerated 

 myelin is removed somewhat more rapidly, though even here not 

 so rapidly as in the peripheral nerves after section. With pro- 

 nounced inflammation other factors are introduced which would 

 readily account for the more rapid removal of the degenerated 

 myelin; as they have no bearing on the question they need not 

 be considered here. Now, medullated fibers of the cord differ 

 histologically from medullated fibers of the peripheral nerves in 

 that the former do not possess a neurilenuna. After section 

 Wallerian degeneration of the one differs from that of the other 

 only in that the proliferation of the nuclei of the neurilemma 

 sheath and the resulting embryonic nerve fiber are lacking in 

 the fibers of the cord. Infiltrating phagocytes are found in 

 degeneration in both cases. 



It is clear then that the rapid multiplication of the nuclei of 

 the neurilemma sheath introduces a factor which is responsible 

 for the rapid removal of the degenerated myelin. It is probable 

 that the protoplasmic activity, represented by the multiplying 

 nuclei and the accumulation of protoplasm around these, is di- 

 rectly concerned with the rapid resorption of the degenerated 

 myelin. 



I have no evidence suggestive of a further activity of the 

 embryonic nerve fiber and its nuclei and this phase of the sub- 

 ject was not taken up. A definite zone rich in protoplasm was, 

 however, observed around the nuclei on the embryonic nerve 

 fibers of the sciatic of fowl No. 9, G. In this protoplasm, dis- 

 crete granules were to be observed in preparations stained with 

 Mallory's phosphomolybdic acid hematoxylin for axis cylinders. 

 These granules have been noted by Reich and others. According 

 to Stroebe ('93), Nageotte ('11) and others they bespeak an 

 activity of the nuclei concerned in the development of a new 

 medullary sheath. 



This view in one form or another has been frequently advo- 

 cated, both as an hypothesis and as an interpretation of the fact 

 that, as pointed out by Stroebe ('93), the protoplasm which 



