3-i-l: Shoatli Cells nnd Axoiio Sheaths in the (\^ntrnl Xervous System 



white suhstanco of the spinal cord, from both of which the myelin has 

 been removed, it is evident at once that, whatever the detailed structure 

 of the sheaths of the two, the framework of the peripheral medullary 

 sheaths is somewhat stronger and heavier than that of the sheaths of 

 the central fiber. This is true for human material and is especially true 

 for the hog. The comparison may usually be made very readily with 

 sections of the spinal cord, for nearly always portions of the ventral and 

 dorsal roots have remained attached to the cord and, involved in the 

 sections, are subjected to the identical technique in staining,' etc., as the 

 cord itself. In the peripheral nerve proper the framework of the medul- 

 lary sheath is slightly heavier than in the nerve roots close to the pia 

 mater. The nerve roots also do not possess the heavy connective tissue 

 investments of the nerve outside the dura mater. Furthermore, in the 

 hog the framework of the medullary sheath, both in the peripheral and 

 central system, is apparently heavier than in man and the other verte- 

 brates more usually studied. This is coincident with the well-known fact 

 that in the hog the fibrous tissue framework of the organs, especially 

 white fibrous and reticular tissue, is peculiarly abundant. 



Under higher magnification the framework of the medullary sheaths 

 of the hog shows a structure and arrangement capable of an interpreta- 

 tion somewhat different from that usually given. The structure cer- 

 tainly differs considerably from that pictured by Wynn. Wynn, however, 

 used the Weigert staining method for medullated fibers and many of the 

 appearances to be obtained by this method suggest that it is somewhat pre- 

 cipitative in its action upon the medullary sheath or that it may be classed 

 among the impregnation methods. Its tendency certainly is to clog the 

 finer structures rather than merely to dye them. Wlassak in his study 

 of the origin of the myelin claims that the Weigert method stains only 

 one substance of the medullary sheath. This substance he calls " cere- 

 hriii" and states that it is one of the constituents of the myelin. In 

 this case, as Hatai points out, Wynn pr-obably did not study the real 

 framework of the sheath, the neurokeratin network of Hatai, but rather 

 obtained pictures indicating the distribution of the cerebrin. 



As stained by the Benda neuroglia method, the framework of the me- 

 dullary sheath of the hog spinal cord appears as represented in Fig. 7. 

 This figure contains fibers from both transverse and longitudinal sections 

 of the cord. Each group was taken from an area near the periphery of 

 the section or in the neighborhood of the pia, for the reason that near 

 the periphery the framework appears heavier than toward the center and 

 is always less collapsed and shrunken, due perhaps to better or earlier 

 fixation near the surface of the specimen. It is seen that in transverse 



