DEGENERATION AND REGENERATION OF NERVES 85 



doubt about the identity of the structures. "When it is remem- 

 bered that the axis cylinder in advanced degeneration is often 

 quite difficult to stain, it is not surprising that such clear pic- 

 tures as the above (fig. 17) were not frequently found. The 

 tortuous course of the new axis cylinder around the globules, 

 as well as the different focal levels of fragments of the old, makes 

 it extremely difficult to get a photomicrographic representation 

 which will show both structures in one picture. Figure 18 shows 

 a fragment of the old axis cylinder, a' , inclosed within a large 

 globule of degenerated myeUn, m, in close proximity to the new 

 axis cylinder a. In figures 19 and 20 the same condition is 

 shown: a', the fragment of the old axis cylinder; m, a globule of 

 degenerated myelin and a, the new axis cylinder. It is more 

 frequently the case that the remains of the old axis cylinder 

 are represented only by a mass of granules or fragments enclosed 

 within the globule. 



Further confirmation of these observations was readily ob- 

 tained by a stud}^ of cross-sections of the sciatic of tkese same 

 fowls. In such sections the new axis cylinder could be seen at 

 one side of the myelin glol)ules while segments or fragments of 

 the old were to be seen within the globule. In some fibers the 

 new axis cylinder was a very small structure, 0.5 ju or less in 

 diameter, and located quite at the periphery of the sheath. In 

 other fibers it was larger and with its surrounding concentric 

 lamellae occupied an equal proportion of the sheath with the 

 globules of degenerated mj^elin. Figure 21, fowl No. 54, shows 

 a new axis cylinder, a, the old axis cylinder, a', and a globule of 

 degenerated myehn, vi, in the same cross-section. Figure 22 — 

 fowl No. 38 — shows a large new axis cylinder, a, with its con- 

 centric lamellae, s, by the side of the old axial tube, a; a' is also 

 surrounded by concentric lamellae and no large globules of 

 myelin are seen here. It is probable that this is a section of a 

 nerve devoid of myelin globules at this place and in which the 

 axis cylmder has degenerated as a result of its interruption by 

 myelin globules at another level. Figures 23 and 24 are photo- 

 micrographs respectively of the same preparations as figures 21 

 and 22. 



