408 CHAPTEB XXXill. 



saturated solution of cyanide of mercury, hardens iu 10 per 

 cent, formol, and stains sections of frozen material by 

 Heidenliain's iron hsematoxylin. 



780, Weigbet's Methods. — There have been in all throe 

 methods of Weigert — the 1884 method, the 1885 method, 

 and the 1891 method. 



The 1884 method {Fortschr. d. Med., 1884, pp. 113, 190; 

 Zeit. wiss. Mile, 1884, pp. 290, 564), which depends on the 

 formation of a chrome lake of heematoxylin, may be con- 

 sidered to be superseded. Not so the two others, which 

 depend on the formation of a copper lake in addition to the 

 chrome lake. 



781. Weigeet's 1885 Method {Forlschr. d. Med., 1885, 

 p. 136 ; Zeit. wiss. Mik., 1885, pp. 399, 481 ; Ergehnisse der 

 Anatomie, vi, 1896 [1897], p. 10). — The tissues are to be 

 hardened in bichromate of potash. Weigeet takes {Ergeh- 

 nisse, ]). 10) a 5 per cent, solution, and if time is an object 

 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 (Ergehnisse, 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 ; and these are ripe. 



More lately {ibid., p. 14) he added to the bichromate solution 2 per 

 cent, of chrome alum or of fluoride of chromium, which hastens the 

 hardening, so that small specimens become brown and ripe in four to 

 five days, without stoving. 



After hardening, the preparation is imbedded in celloidin 

 (if desired ; imbedding is not obligatory) and hardened in 

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

 days, in an incubating stove, into saturated solution of 

 neutral acetate of copper diluted with one volume of water. 

 By this treatment the tissues become green and the celloidin 

 bluish-green. The preparation may then be kept till wanted 

 for sectioning in 80 per cent, alcohol. 



