CHAPTER III 

 SPECIAL NEUROLOGICAL STAINING METHODS 



Weigert's Method of Staining Medullated Nerve Fibres 



In preparing material for the Weigert method, two points are to 

 be kept in mind: ist, proper fixation and preservation of the myelin 

 sheaths; 2d, treatment (mordanting) with a reagent which enters 

 into combination with the myelin, the result being that the myehn 

 sheaths stain specifically with haematoxylin . Formahn fulfils the 

 first requirement, the bichromates the first and second. Consequently 

 the material may be fixed and hardened in bichromate, and, if not 

 to be used immediately, is best kept in formahn to avoid overharden- 

 ing. Or the material may be fixed and kept in formalin and impreg- 

 nated with the bichromate before using, the latter being done before 

 dehydrating in alcohol. Further mordanting, which is usually done, 

 especially when the material has been kept for some time in formahn 

 or alcohol, is for the purpose of intensifying the stain. 



Material is fixed in one of the following fluids: 



(a) ]\Iuller's fluid (page 7). 



(b) Potassium bichromate, 5-per-cent. aqueous solution. 



(c) Formalin, lo-per-cent. aqueous solution. 



(d) Formahn, i volume; potassium bichromate, 5-per-cent. 

 aqueous solution, 9 volumes. 



In ^Miiller's fluid or in plain potassium-bichromate solution a 

 hardening of two days to four weeks is required; in formahn or 

 formahn-bichromate from a week to ten days is suflicient. All 

 material is better kept until used in 5-per-cent. to lo-per-cent. 

 formalin solution than in alcohol. The specimens are then hardened 

 in graded alcohols, embedded in celloidin, and sections cut in the 

 usual way. Material fixed in formahn should be placed for several 

 days in the following: 



Chrome alum, i gm. 



Potassium bichromate, 3 gm. 



Water, 100 c.c. 



before hardening in alcohol. 



33 



