308 RETINA, TNNER EAR, NERVES. 



Nerves. 



650. Weigert's Method for Medullated Nerves (Fortschr. d. 

 Med., 1884, pp. 113, 190; 1885, p. 136; Zeit.f. wiss. Mik., 

 1884, pp. 290, 564; 1885, pp. 399, 484). The ordinary 

 methods of staining with haematoxylin depend on the produc- 

 tion of an aluminium lake of haBmatoxylin. Weigert's method 

 depends on the formation of another lake, a chromium or copper- 

 lake. In consequence of the formation of these lakes, haema- 

 toxylin acquires the property of staining the myelin of nerves 

 in a quite specific way. 



In Weigert's process the formation of these lakes takes 

 place in the tissue itself. He proceeds now (I pass over the 

 earlier form of the method) as follows : The tissues are to be 

 hardened in bichromate of potash (the solutions of Miiller or 

 Erlicki will do as well, so far as I know). The hardening 

 need only be carried to the point at which the tissues have 

 acquired a broivn, not a green, colouration (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, MI id 

 the celloidin bluish-green. The mordaiitage 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 



Hsematoxylin . . . . . 0'75 to 1 part. 



Alcohol ....... 10 



Water ....... 90 



Saturated solution of lithium carbonate . 1 



(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 

 luBinatoxylin solution.) 



sections remain in the stain for a length of time that 

 varies according to the natuiv of tin- tissues : Spinal cord, 



