4S4 CilAWKU XXX[V. 



For tlje very complicatad platiiiaiu-sul33titufcion i^rocesses of Robert- 

 son and Macdonald see Jourii. Meiit. Sc/., xlvii, 1901, p. 327 ; ov Jo lira. 

 Hoy. Mic. Soc, 190:2, p. 601. 



83[). Ziehen's Gold and Sublimate Method {Neurol. Centralb., 

 X, 1891, p. 65). — Small jDieces of fresh material are thrown 

 into a large quantity of a mixture of 1 per cent, sublimate 

 solution and 1 per cent, chloride of gold solution in equal 

 parts. They remain therein for at least three weeks, 

 preferably for several months (up to five), by which time 

 they will have become of a metallic red-brown colour. They 

 are gummed on cork and sectioned witliout imbedding. The 

 sections are treated either with Lugol's solution diluted with 

 four volumes of water, or with dilute tincture of iodine, until 

 duly differentiated, then washed and mounted in balsam. 

 Both medullated and non-medullated nerve-fibres are stained, 

 also nerve and glia cells and their processes. 



831. Keohnthal's Lead Sulphide Impregnation [Neurol. Cen- 

 tralb., xviii, 1899, No. 5; Zeif. iviss. Bilk., xvi, 1899, p. 235) 

 consists in treating tissues first with formate of lead and 

 then with hydric sulphide. The formate is prepared by 

 dropping formic acid slowly into solution of acetate of lead. 

 White crystals of formate of lead are abundantly formed ; 

 the mother liquor is filtered off, and the crystals are dis- 

 solved to saturation in water. The solution is mixed with 

 an equal volume of 10 per cent, formol ; pieces of brain or 

 spinal cord are put into the mixture for five days, and are 

 tlien brought direct into a mixture of equal parts of 10 per 

 cent, formol and hydric suliDhide solution. After five days 

 therein they are cut in celloidin, and the sections mounted in 

 xylol-balsam under a cover. They seem to be quite perma- 

 nent. Nerve-cells as well as nerve-fibres are impregnated. 

 The impregnation is a very complete one. 



Corning (Anat. Anz., xvii, 1900, p. 108) hardens the 

 tissues with 10 per cent, formol before bringing them into 

 the formol-formate mixture, and so obtains better results. 

 He obtains his formate of lead direct from Meeck [Plumhum 

 formicicum). He prefers to cut without imbedding. Other 

 details loc. cit. 



