222 CHAPTER XVII. 



witli one part 2 per cent, osmio acid, washes, puts for two 

 to six hours into 1 per cent, 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 

 reducti'tn of the gold. 



Thus Bastian employed a solution of gold chloride of a 

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

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

 and water fcepi tvarm. 



Henocque {Arch, de I'Auat. et de la Physiol., 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° G. Reduction is effected very rapidly, 

 sometimes in a quarter of an hour. 



HoYEii [Arch. mih. Aiiat., 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 j^yi'ogallic acid developing solution, 

 such as is used in photography, or in a wann 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 Leitungshalmen in Gehirn, 1876 ; Arch. Aiiat. 

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

 caustic soda. 



NESTEEOiTSKY treats impregnated preparations with a drop 

 of ammonium sulphide, and finishes the reduction in glycerin 

 (quoted from Gierke's Farherei ?.. m,%k ZwecJcen). 



BoHM reduces in PritcJiard's solution — amyl alcohol, 1 ; 

 formic acid, 1 ; water, 98. 



