Irving HarJesty 347 



two general types with, however, all gradations between the two. In 

 Fig. 8, A and B, there are represented examples of the extremes of the 

 two types. They are chosen from among the dorsal root fibers of the 

 adult specimen and show the nature of the framework as brought out by 

 the Benda stain. The majority of the fibers in both the nerve roots show 

 an arrangement of the framework conforming in various degrees to type 

 A. The framework of type B, though somewhat heavier in structure, 

 conforms quite closely with the general type found in the spinal cord. 

 To illustrate type B, a piece of fiber involving a node of Ranvier (nR) 

 was chosen to show the interesting fact that the lamellated reticulum of 

 the sheath framework is not interrupted at the node. Not only are both 



J5 





c 

 ai 



-iC^^S. 



Fig. 8. Transverse and longitudinal sections of dorsal root (peripheral) 

 nerve fibers from same preparations as Fig. 7. Showing extremes (A and B) 

 of the two general types of framework of medullary sheaths, sch = sheath 

 of Schwann; «^ nerve corpuscle; ni^^node of Ranvier; c = cone arrange- 

 ments of framework; other letters =: same as in Fig. 7. Use hand lens to 

 observe details cited, x 550. 



the outer and inner " membranes " continuous through the node, as 

 pointed out by Hatai, but also some of the intermediate lamella) pass 

 from one internode to the other. From the fact that but slight condensa- 

 tion is apparent at the nodal constriction, it is probable that the frame- 

 work is less abundant at that point. Close examination shows that the 

 reticulum suddenly narrows clown by both a diminution in the number 

 of its lamellae and a diminution in the size of its meshes. The same 

 general behavior is also apparent at the nodes in fibers of type A. 



Sheath frameworks of the type B seem less frequent in the peripheral 

 nerves proper than in the nerve roots within the dura mater. So far, 

 however, I have examined sections of only one piece of peripheral nerve 



