412 NERVOUS SYSTEM SPECIAL METHODS. 



while on the section. As soon as this has become quite transparent, 

 the cajeput oil is dried off with filter paper, the section thoroughly 

 washed with benzol and covered with a drop of thick xylol-colo- 

 phonium, rendered more fluid by passing the slide carefully over a 

 flame, and quickly covering the section with a thin cover-glass before 

 the colophonium sets again by cooling. 



827. Suggestions regarding the Carrying-out of Nissl's Method 

 (as deduced from NISSL'S papers ; see chiefly Enz. d. mikr. TecJin., ii, 

 1910, pp. 252 280, and the references therein quoted at p. 287). 

 For the fixation of tissues alcohol should be almost exclusively 

 used. Formalin, mixture of formalin and alcohol, sublimate and 

 mixture of the same with alcohol or picric acid and the like, nitric 

 acid may be occasionally employed, but no particularly good results 

 can be expected from them. These are, however, somewhat better if 

 tissues are placed for some time in alcohol after fixation with one 

 or the other of the above reagents. This applies particularly to 

 formalin material, which can be kept with advantage for many 

 weeks, and even months, in repeatedly changed 96 per cent, alcohol. 

 The bichromates of potassium and ammonium and mixtures con- 

 taining chromic' salts, though useful for other purposes, should be 

 entirely avoided for cytological investigations in Nissl's sense. See 

 on this subject also BURCHARDT, La Cellule, xii, 1897, p. 337. 



If tissues are too brittle to be sectioned without embedding, or 

 if embedding is for any other reason desirable, one should have 

 recourse to celloidin, paraffin being used only when unavoidably 

 necessary or for special purposes. Pieces to be embedded in celloidin 

 are not to be passed through alcohol-ether, but directly from absolute 

 alcohol into thin celloidin. Embedding should, in any case, be carried 

 out as quickly as possible. 



Sections of material which was not fixed in alcohol and of em- 

 bedded tissues, however fixed, stain, as a rule, very poorly by 

 Nissl's soap-methylene-blue method ; but good and even excellent 

 results can be obtained by staining such sections with watery 

 solutions (generally 0-5 to 1 per cent.) of toluidine blue, thionine, 

 Unna's polychrome methylene blue, dahlia violet, vesuvine, neutral 

 red, magenta red, Azur I, Azur II, and the like. 



If one of such stains is used, it need not be warmed until 

 bubbles come to the surface, but only until vapour arises. For 

 the differentiation pure 96 per cent, alcohol, viz., without any 

 addition of anilin oil, should be used. In this connection I find 

 that very good results can be obtained from material embedded in 



