DEGENERATION AND REGENERATION OF NERVES 89 



From these facts it is clear that neither the nuclei of the sheath 

 of Schwann nor the embryonic nerve fiber could have taken 

 any part in the formation of the new axis cylinder. Conse- 

 quently auto-regeneration in so far as it signifies the formation 

 of a new axis cylinder by the embryonic nerve fiber does not 

 obtain with fowls in regeneration after paralysis from polished 

 rice. 



The same observations which show that the new axis cylinder, 

 in these experiments, is not acquired through auto-regeneration, 

 also demonstrate that it is attained by outgrowth. The pres- 

 ence of a new axis cylinder and segments of the old in the same 

 old medullary sheath; the presence of two new axis cyUnders in 

 an old sheath, and the oc»urrence of a new axis cyhnder with 

 an outgrowing branch, and of an outgrowing axis cylinder with 

 an end bulb, can only mean that, in the absence of auto-regen- 

 eration, the new axis cylinder has grown out from its central 

 stump. ^ 



Regeneration in the cord 



Before considering the possibihty of regeneration in the fibers 

 of the cord, it is necessary to refer to the degenerative changes 

 in the medullated fibers and nerve cells of the cord described by 

 me in a recent study of "Polyneuritis Gallinarum" ('12). Here 

 it was found that a very small per cent of the fibers of all columns 

 of the cord presented as advanced myehn degeneration, as the 

 fibers of the peripheral nerves. A still smallei; per cent of the 

 fibers also showed a disintegration or breaking up of the axis 

 cylinder. The nerve cells of the ventral horn and the basal 



^ The question naturally arises, at what point does this outgrowth of the axis 

 cylinder begin? I have not been able to answer this satisfactorily. One would 

 suppose that outgrowth would begin at the peripheral end of that segment of 

 the axis cylinder (still connected with the nerve cell) which did not undergo 

 degeneration; if such a segment exists. As stated below, I have not been able 

 to determine if that portion of the axis cylinder running between the anterior 

 horn cells and the periphery of the cord ever shows segmentation, such segmen- 

 tation not having been observed. Both ventral and dorsal nerve roots, on the 

 other hand, have been frequently observed in which segmentation and disinte- 

 gration of the axis cylinder and clumping of the myelin were clearly visible. 



