CHAPTER XXXiL. 



NEBVOUS yYSTEM — OYTOLOGIOAL METHODS. 



766. Introduction. — The ordinary methods of cytology are 

 of course available for nerve-cells. Bat there are two 

 characteristic elements of these cells — the tigroid substance, 

 and the system of neuro-fibrils, which require^ for minute 

 study, special methods such as the following. 



A. Methods for Cells, demonstrating Tigroid Suhdance. 



757. Tigroid substance is a markedly basophilous element, 

 occurring in the form of granules or larger irregular blocks 

 known as the " bodies of Nissl." It takes up basic anilin 

 dyes, but does not hold them with such special energy, as 

 for example, the chromatin of nuclei. It is usually stained 

 by the regressive method, with very careful differentiation. 

 The material is usually fixed with alcohol, formol, or subli- 

 mate. Van Gehuchten and Nelis {La Cellule, xiv, 1898, 

 p. 374) recommend Gilson's mixture, § 69. 



All the following stains have the defect of Iceeping hadlij ; 

 they generally do not last more than a few months. 



758. Nissl's Methylen-blue Method [Neurol. Centralb., 1894, 

 p. 508). — Fresh material is hardened in 96 per cent, alcohol, 

 and sectioned without imbedding. The sections are floated 

 on to the following stain poured into a watch-glass : 



Methylen blue (Methylenblau B. pat.) . 3-75 parts. 



Venice soap ..... r75 „ 



Distilled water 1000-0 „ 



(This stain should not be used fresh, but kept for at least 

 three months.) 



The watch-glass is warmed over a flame to about 65° to 

 70° C. till bubbles are given off. The sections are then 

 brought for an instant (5 to 20 seconds) into a mixture of 



