No. 3-] PERIPHERAL NERVES. 713 



ment of the medullary sheaths about the newly formed axis 

 cylinders, as the anilin-blue safranin method (used for staining 

 sections made from all nerves where the process of regeneration 

 was made the subject of study, from 21 to 182 days after 

 implantation) is not a suitable stain for making out the origin 

 of this sheath. In the author's sections prepared after this 

 method the medullary sheath is not differentiated until a time 

 when it has obtained some degree of prominence. Stroebe 

 recognizes in the delicate pale blue sheath, which surrounds the 

 more deeply stained axis cylinders, a structure already referred 

 to several times, the beginning of the layer of myelin. He 

 states that in sections stained after Weigert's haematoxylin 

 method " the young fibres are stained deeply black ; they pos- 

 sess, therefore, at their first appearance a medullary sheath, the 

 pale blue layer in anilin-blue preparations ; accordingly, the 

 medullary sheath is an attribute of the young fibres from the 

 time of their first appearance." The diagrams illustrating 

 Willard's articles show that the medullary layer must be devel- 

 oped at a very early stage ; as in his preparations, stained 

 with Weigert's haematoxylin, the nerve fibres were stained 

 deeply black at a time when he v/as first able to recognize them. 

 Biinger states that *' the myelin is formed as a narrow continu- 

 ous sheath, which stains black in osmic acid, and secondarily 

 as a thicker layer which develops in segments, and at a later 

 stage fuses with the former (an die erste anschliesst und mit 

 derselben verschmilzt)." 



If the narrow continuous sheath, which assumes a pale blue 

 color in the anilin-blue safranin stain, is to be regarded as the 

 anlage for the medullary layer, I think that we must admit 

 that in its first development, it must have a slightly different 

 chemical structure than it does at a later stage ; for when it is 

 more fully developed, in preparations stained by the above 

 method, it has a yellowish or an orange color, even after much 

 of the safranin has been washed out of the sections, as may be 

 seen from Stroebe's and my own diagrams. The virtue of the 

 anilin-blue safranin method, is to be found in its clear axis 

 cylinder differentiation, and was for this reason used. The 

 time at my disposal did not admit of my making duplicate 



