WEIGERT'S METHOD. 363 



acquired a brown, not a green, coloration (but green tissues 

 may be used, provided they have once passed through the 

 brown stage) . The preparation is then (but this is not neces- 

 sary) imbedded by infiltration with celloidin, 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 incubat- 

 ing stove. By this treatment the tissues become green, and 

 the celloidin bluish green. The mordantage of the tissues is 

 now terminated, and the preparation may be 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 car- 

 bonate ...... 1 part. 



(A trace of any other alkali may be added in the place of lithium carbonate. 

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

 solution.) 



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 



Borax ...... 2*0 parts. 



Ferricyanide of potassium . . 2*5 



Water 200-0 



They remain in the solution until they are decoloured to 

 the right degree that is, until complete differentiation of the 

 nerves (half an hour to several hours) and are then rinsed 

 with water, dehydrated with alcohol, and mounted in balsam. 

 They may be previously stained, if desired, with alum-carmine 

 for the demonstration of nuclei. 



For very difficult objects, such as pathological nerves, the decolouring 

 solution should be diluted with water, and the immersion in it prolonged. 

 GELPKE (Zeit. f. wiss. Mik., 1885, p. 489) states that for transverse sections 

 of atrophied nerves the solution should be diluted with fifty volumes of 



