NEUROLOGICAL METHODS. 397 



hardens in a stove. (Other bichromate mixtures will do, 

 e. g. Miiller's, Kultschizky's, Zenker's ; Erlicki's is not to be 

 recommended). The tissues are " ripe " for staining when 

 the hardening has been carried to a certain point. They 

 are first (Ergebnisse, p. 13) yellow, without differentiation of 

 the grey matter from the white ; these are unripe. Later 

 they show the grey matter light brown, the white matter 

 dark brown (owing to reduction of a part of the bichromate 

 to a chrome oxide in the medullary sheaths) ; these are 

 " ripe." If the hardening be continued " all the more 

 highly oxidised chrome will pass into the lower stage of oxida- 

 tion, and the tissues will become green. " The tissues are 

 then over-ripe, and cannot be used for myelin-staining without 

 mordanting with copper or the like. 



After due hardening, the preparation is imbedded by in- 

 filtration with celloidin (if desired : imbedding is not obliga- 

 tory) and the celloidin block fastened on cork and hardened 

 in the usual way. The hardened block is put for one or 

 two days into saturated solution of neutral acetate of copper 

 diluted with one volume of water, the whole being kept at the 

 temperature of an incubating stove. By this treatment the 

 tissues become green and the celloidin bluish green. The 

 mordantage of the tissues is now terminated, and the pre- 

 paration may ba kept till wanted for sectioning in 80 per 

 cent, alcohol. 



Sections are made with a knife wetted with alcohol, and 

 are brought into a stain composed of 



Haematoxylin . . . 0*75 to 1 part. 



Alcohol ...... 10 parts. 



Water 90 



Saturated solution of lithium carbonate 1 part. 



(A trace of any other alkali may be added in the place of lithium car- 

 bonate. The object of adding a little of some base is to " ripen " the 

 haematoxylin solution ; or the solution may be made up with hsematein, 

 and the alkali omitted.) 



The sections remain in the stain for a length of time that 

 varies according to the nature of the tissues : spinal cord, 

 two hours ; medullary layers of brain, two hours ; cortical 

 layers, twenty-four hours. 



They are then rinsed with water, and brought into a de- 

 colourising solution composed of 



