SPECIAL STAINS. 403 



cylinders. This method is based on that of FLECHSIG (see 

 228), which I suppress, as it gives less certain results. Freud 

 proceeds as follows : Sections of material hardened in solu- 

 tion of Erlicki (which may be followed by alcohol without 

 hindrance to the impregnation) are washed with water, and 

 put for three to five hours into 1 per cent, solution of gold 

 chloride. After again washing with water they are treated 

 for three minutes with a solution of 1 part of caustic soda in 

 5 or 6 of water. They are then drained (not washed) and 

 brought into 10 or 12 per cent, solution of iodide of potassium. 

 After from five to fifteen minutes therein they are washed 

 with water, dehydrated, and mounted in balsam. (In the case 

 of objects that stain easily it is useful to dilute the gold solu- 

 tion with a volume or two of alcohol ; the stain is more highly 

 selective.) 



BECKWITH (Journ. Roy. Mic. Soc., 1885, p. 894) modifies this process by 

 intercalating a treatment for thirty minutes with 10 per cent, solution of 

 carbonate of potash between the soda and the iodide. 



769. ZIEHEN'S gold and sublimate method (Neurol. Centralb., 

 x, 1891, No. 3, p. 65; Zeit. f. wiss. Mik., viii, 3, 1891, p. 385) 

 gives the following derivative of Golgi's sublimate method as 

 an improvement on it : Small pieces of fresh material are 

 thrown into a large quantity of a mixture of 1 per cent, sub- 

 limate 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 without imbedding. The 

 sections are treated either with solution of Lugol ( 66) 

 diluted with four volumes of water, or with dilute tincture of 

 iodine, until duly differentiated, which will require more or 

 less time according to the thickness of the sections. They 

 are then washed and mounted in balsam. The result is a 

 bluish-grey impregnation ; both medullated and non-medul- 

 lated nerve-fibres are stained, also nerve- and glia-cells and 

 their processes. 



770. UPSON'S Methods (MERCIEK, in Zeit.f. wiss. MiJc., vii, 4, 

 1891, p. 474 : I pass over the older methods given in Neurol. 

 Centralb., 1888, p. 319; and Zeit. f. wiss. Mik., 1888, 

 p. 525). 



