SPECIAL STAINS. 333 



stated to be simpler than Weigert's. The tissues are hardened in a liquid 

 composed of : Water, 100 c.c. ; chromic acid, 075 g. to 1 g. ; acetate of 

 copper, 5 g. Human cord requires six to eight days ; the cord of the dog, 

 three to four ; brain of dog, fifteen to eighteen. They are then dehydrated 

 and imbedded in celloidin. Sections are stained in a liquid made by adding 

 seven to eight drops of a 5 per cent, solution of haematoxylin in absolute 

 alcohol to about 30 c.c. of alcohol. After two hours they are brought into a 

 mixture of eight drops of hydrochloric acid with 100 c.c. of absolute alcohol, 

 and washed therein until the white substance is seen to be differentiated 

 from the grey. They are washed out for twenty minutes or more in water, 

 dehydrated, and mounted. The sections may be double-stairfed with borax- 

 carmine. 



FREUD'S gold method (Arch. f. Anat. u. Phys., 1884, p. 453) 

 may be used for controlling the results obtained by Weigert's 

 process, find for obtaining an impregnation of axis cylinders. 

 This method is based on that of FLECHSIG (see 211), which I 

 suppress, as it gives less certain results. Freud proceeds as 

 follows : Sections of material hardened in solution 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, de- 

 hydrated, and mounted in balsam. (In the case of objects 

 that stain easily, it is useful to dilute the gold solution 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. 



The gold method is one of the most important methods for 

 the study of the liner nerve fibrils of the spinal cord. The 

 instructions given by GEBLACH (Strieker's Handb., p. 678) 

 liave been already quoted, ante, 211, p. 117. 



BOLL (Arch. /. Psych, u. Nervenkr., iv, p. 42 ; GIERKE, Zeit. 

 f. /r/.v.v. J/ /'/,-., 1884, p. 403) makes the following observations 

 on (Jerlac'n's process: The hardening in bichromate ought 

 not to be prolonged further than is absolutely necessary, for 

 after eight days the elective susceptibility of the tissues for 

 gold impregnation begins to diminish, and after fifteen days 



