DEGENERATION AND REGENERATION OF NERVES 93 



sheaths into globules of degenerated myelin and a segmentation 

 or granulation of their axis cyhnders. No multiplication of the 

 nuclei of the neurilemma sheath could be observed and conse- 

 quently no embryonic nerve fibers or Band-fasern. 



During recovery these degenerated fibers attained new axis 

 cylinders and the medullary sheaths returned to normal. In 

 other words, regeneration has been observed to follow degener- 

 ation in meduUated nerve fibers without passing through the 

 embryonic nerve fiber or Band-faser stage. 



By prolonging the degenerative process there resulted a multi- 

 plication of the nuclei of the neurilemma sheath. This and other 

 experiments described tend to show that the embryonic nerve 

 fiber may be coincident with a late stage of degeneration in 

 medullated nerve fibers. It may not represent an early stage 

 of regeneration and its presence does not signify an attempt at 

 regeneration on the part of the medullated nerve fiber. 



In the absence of the embryonic nerve fiber, the degenerated 

 myehn was absorbed with extreme slowness, persisting as drop- 

 lets after 1 year and 14 days. On the other hand, where the 

 embryonic nerve fiber was formed the degenerated myelin quickly 

 disappeared from the fiber. The conclusion is reached that the 

 proliferating nuclei of the neurilemma sheath participate in the 

 resorption of the degenerated myehn. 



In regeneration a new axis cylinder was attained by outgrowth 

 and in the absence of the embryonic nerve fiber. The new axis 

 cylinder grew down the old medullar}^ sheath which latter still 

 contained large globules of degenerated myelin and fragments 

 of the old axis cylinder. The outgrowing axis cylinder was seen 

 to branch, and in cross-sections of the nerves two new axis cylin- 

 ders were observed within the same old medullary sheath. The 

 embryonic nerve fiber could, of course, play no part in the for- 

 mation of the new axis cylinder either by auto-regeneration or 

 by outgrowth. 



No indications of regeneration were observed in the fibers of 

 the spinal cord. 



Anatomical Laboratory, The University of Chicago, 

 June 28, 1913. 



