SPECIAL NEUROLOGICAL STAINING METHODS 35 



copper-acetate solution. After rinsing in water the sections are 

 stained in ha^matoxylin as in the ordinary Weigert method. The 

 Hthium carbonate may, however, be omitted. They are then washed 

 and transferred to a 0.25-per-cent. sokition of potassium permanga- 

 nate, where they remain from one-half to two minutes, after which 

 they are again washed and ])laced in the following: 



Oxalic acid, i gm. 



Potassium sulphite, i gm. 



Water, 200 c.c. 



In this solution differentiation takes place, the medullary sheaths 

 remaining dark, while the color is entirely removed from the rest of 

 the tissue. If the section is still too dark, it may again be carried 

 through the permanganate and oxalic-acid solutions, rinsing in water 

 between changes, until sufhciently decolorized. 



All formaUn-lixed material is best stained by the Weigert-Pal 

 method. An intensification of the stain, especially of the very fine 

 fibres, may sometimes be obtained by placing the sections for a min- 

 ute in a 0.5-per-cent. aqueous solution of osmic acid before 

 decolorizing. 



*&• 



Marchi's Method por Staining Degenerating Nerves 



Small pieces of tissue are fixed and hardened for from seven to 

 ten days in Miiller's fluid. Thin sHces of the tissue are then trans- 

 ferred to a solution of one part i-per-cent. osmic acid and two parts 

 Mtiller's fluid, in which they remain from two to seven days. After 

 embedding and sectioning in the usual manner, sections are mounted, 

 usually without further staining, in xylol-balsam. The treatment 

 with Miiller's fluid so affects the normal medullary sheaths that they 

 will not take the osmic-acid stain, but appear yellowish-brown, w^hile 

 the degenerating sheaths (probably fatty) stain black. The result 

 is a positive picture of stained degenerating fibres in contrast with the 

 stained normal and unstained degenerated fibres as seen after Weigert 

 staining. Another advantage of the Marchi method is that, as the 

 picture is a positive one, an early or sHght degeneration may be recog- 

 nized which would escape notice in material stained by Weigert's 

 method; on the other hand, in a long-standing degeneration w^hen the 

 medullary sheaths have completely disappeared and their places have 

 been taken by connective tissue, there being no degenerated myehn 

 remaining, the Marchi method is inappKcable. 



