152 METALLIC STAINS (IMPREGNATION METHODS). 



says that a simple 5 per cent, aqueous solution of tannin gives excellent 

 results, sometimes superior to those obtained by the " developer "). See 

 my note in Zeit.f. wiss. Mik., ix, 1892, p. 185 ; also op. cit., p. 316. 



HEEMANN (Arch.f. Mik. Anat., xxxvii, 1891, p. 569 ; Zeit.f. wiss. Mik., 

 viii, 3, 1891, p. 367) has been using with success crude pyroligneous acid for 

 reducing the osmium in preparations fixed in his platino-aceto-osmic mixture 

 ( 36A). The acid should be allowed to act for twelve to eighteen hours. 



ALLEN (Quart. Journ. Mic. Sci., xxxiv, 1892, p. 75) has been treating in 

 the same way objects fixed in FLEMMING'S solution, and attributes the method 

 to VON MAHBENTHAL. 



The method of BBOSICKE (Centralb.f. d. med. Wiss., 1879, p. 873 ; Zeit. 

 f. wiss. Mik., i, 1884, p. 409) consists in treating osmium objects for twenty- 

 four hours with a solution of 1 part of oxalic acid in 15 parts of water- 

 This gives a Burgundy-red stain. It is necessary that the objects be washed 

 and brought into the oxalic acid as soon as possible after the treatment with 

 osmium, as if the osmium has once begun to blacken them, the oxalic acid 

 is powerless afterwards to redden them. 



234. Palladium Chloride (F. E. SCHTJLTZE, see ante, 52 and 84). 

 Prussian Blue (see LEBEE, Arch. f. Ophthalm., xiv, p. 300 ; EANVIEE, 

 Traite, p. 108). Cupric Sulphate (see LEBEE, ibid.). Lead Chromate 

 (see LEBEE, ibid.). Sulphides (see LANDOIS, Centralb. f. d. med. Wiss., 

 1885, No. 55 ; and GIEEKE, in Zeit. f. wiss. Mik., i, 1884, p. 497). 

 Molybdate of Ammonium (Merkel ; Krause) (see GIEEKE, Zeit.f. wiss- 

 Mik., i, 1884, p. 96). Impregnation with Fats, Altmann's Method 

 (see post, " Corrosion "). 



