DEGENERATION AND REGENERATION OF NERVES 71 



have shown degenerative changes. This slender fiber with fre- 

 quent nuclei, then, might easily represent a later stage or atrophy 

 of a fiber which failed of regeneration. 



To summarize briefly: Neither embryonic nerve fibers nor a 

 marked multiplication of the nuclei of the neurilemma sheath 

 have been found in degenerating fibers of fowls showing paralysis 

 after 20 to 30 days on polished rice: they have not been observed 

 (with one possible exception) in regenerating fibers of fowls re- 

 covering from this paralysis: embryonic nerve fibers containing 

 droplets of degenerated myelin were found in the nerves of fowls 

 fed for 51 and 60 days on a polished rice diet, and embryonic 

 nerve fibers entirely replaced the nervous elements in the sciatic 

 of a fowl whose leg was undergoing progressive necrosis. 



This chain of evidence seems complete and can leave little 

 doubt as to the significance of the so-called embryonic nerve 

 fiber, Band-faser or protoplasmic band. In each instance except 

 the last we have the embryonic nerve fiber occurring in a nerve 

 which is undergoing progressive retrogression. In fowl No. 78 

 the degeneration was due to mechanical causes. In No. 17, G, 

 and No. 9, G, those few fibers which always showed marked 

 degeneration b}^ the thii'tieth day, regardless of whether symp- 

 toms are manifested or not, had had time for a more advanced 

 degeneration than those fibers of fowls killed at an earlier date. 

 In either case, it was impossible for regeneration to be taking place. 



Thus the conclusion that the embryonic nerve fiber represents 

 a late stage of degeneration is a logical one. Degeneration as 

 used above is meant to imply a retrogressive change in the myelin 

 sheath and axis cylinder. It is to be noted that multiplication 

 of the nuclei of the neurilemma sheath and the resulting embry- 

 onic nerve fiber appear only after degeneration in the axis cylin- 

 der and medullary sheath has advanced to a late stage. As Van 

 Gehuchten points out, the sequence of events in the formation 

 of the embryonic nerve fiber with cytoplasm and cytoplasmic 

 granules around the nuclei must be considered evidence of proto- 

 plasmic activity and in themselves bear a close resemblance to 

 regenerative processes. This, however, does not necessarily imply 

 an attempt on the part of the structure at formation of a new 



