72 S. WALTER RANSON 



branching. The size and characteristic grouping of the non- 

 medullated fibers excludes the possibiUty of their being confused 

 with connective tissue fibers. Moreover it is only in faulty prep- 

 arations that the connective tissue fibers are stained. In the 

 best preparations the connective tissue does not appear fibrillar 

 but finely granular; and the axons stand out clearly from this 

 light yellow, finely granular background. 



If the fibers which have been described cannot be confused with 

 connective tissue, is it possible that they are small medullated 

 fibers? The existence of many very small medullated fibers in 

 the nerves, and the fact that the Cajal method does not give a 

 satisfactor}^ demonstration of the myelin sheaths make this a 

 very pertinent question. In order to test this possibility a com- 

 parison has been made between the axons brought out by Cajal's 

 method and the myelin sheaths stained by the Pal-Weigert 

 method or by that of Stroebe. Since osmic acid does not pene- 

 trate well into nerves of a size required to give a satisfactory 

 silver stain, it could not be used for this purpose. It is not pos- 

 sible to take two immediately successive sections and stain one 

 for axons and the other for myelin sheaths, since each method 

 requires a special treatment of a block of tissue. However, sec- 

 tions which in their original position in the nerve were not 

 separated by more than a few millimeters can be compared. The 

 photomicrographs (figs. 6 and 7) are from adjacent sections of a 

 human sciatic nerve. Fig. 6 from a cross-section stained by the 

 Pal-Weigert method shows the myelin sheaths as dark rings, 

 and brings out as large a proportion of small medullated fibers 

 as can be found anywhere in the section. Fig. 7, from a Cajal 

 preparation, shows the myelin sheaths as colorless rings and the 

 axons, both medullated and non-medullated, as black dots. It 

 was photographed from a field especially rich in non-medullated 

 fibers. The magnification was the same in both cases. This ena- 

 bles one to compare the number of myelin sheaths in one section 

 with the number of axons in an adjoining section of the same nerve. 

 Since the area represented in Fig VI contains a high proportion of 

 small medullated fibers, and since the fibers are not more widely 



