222 CHAPTEK, XVII. 



with one part 2 per cent, osmic acid, washes,, puts for two 

 to six hours into 1 percent, gold chloride in the dark, washes, 

 puts for twelve hours into 25 per cent, formic acid in the 

 dark and then for twenty-four in the light, and mounts in 50 

 per cent, glycerin with 1 per cent, of formol. 



368. Other Methods. The numerous other methods that 

 have been proposed differ from the foregoing partly in 

 respect of the solutions used for impregnation, but chiefly in 

 respect of details imagined for the purpose of facilitating the 

 reduction of the gold. 



Thus BASTIAN employed a solution of gold chloride of a 

 strength of 1 to 2000, aciduated with HC1 (1 drop to 75 

 c.c.), and reduced in a mixture of equal parts of formic acid 

 and water kept ivarm. 



HENOCQUE (Arch, de I'Anat. et de la PkysioL, 1870, p. Ill) 

 impregnates in a 0'5 per cent, solution of gold chloride, 

 washes in water for twelve to twenty-four hours, and reduces 

 in a nearly saturated solution of tartaric acid at a tempera- 

 ture of 40 to 50 C. Reduction is effected very rapidly, 

 sometimes in a quarter of an hour. 



HOYER (Arch. mik. Anat., ix, 1873, p. 222) says that the 

 double chloride of gold and potassium has many advantages 

 over the simple gold chloride. He impregnates in solutions 

 of 0'5 per cent, strength, and reduces in water containing 

 one or two drops of a pyrogallic acid developing solution, 

 such as is used in photography, or in a warm concentrated 

 solution of tartaric acid, at the temperature of an incubating 

 stove. 



I have myself used the double chloride of gold and sodium 

 with good results. 



CIACCIO (Journ. de Microgr., vii, 1883, p. 38) prefers the 

 double chloride of gold and cadmium. 



FLECHSIG (Die Leitungsbahnenin Uchint, 1876 ; Arch. Anat. 

 u. Phys., 1884, p. 453) reduces in a 10 per cent, solution of 

 cniiNtic soda. 



NESTEROFFSKY treats impregnated preparations with a drop 

 of ammonium sulphide, and finishes the reduction in glycerin 

 (quoted from GIERKE'S Fdrberei z. mik Zwecken). 



BOHM reduces in Pritchard's solution amyl alcohol, 1 ; 

 formic acid, 1 ; water, 98. 



