254 CHAPTER XVI1T. 



the reduction of the gold,, and rendering it as complete as 

 possible. 



Thus BASTIAN modified COHNH KIM'S original method by 

 employing a solution of gold chloride of a strength of 1 to 

 2000,, acidulated with HC1 (1 drop to 75 c.c.), and perform- 

 ing the reduction in a mixture of equal parts of formic acid 

 :and water kept warm, heat being an agent that furthers 

 reduction. 



HENOCQUK (Arch, dc I'Anat. 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 re- 

 duces,, with the aid of heat,, in a nearly saturated solution of 

 tartaric acid. The tartaric acid solution must be contained 

 in a well-stoppered bottle. The best temperature for reduc- 

 tion is 40 to 50 C. Reduction is effected very rapidly, 

 .sometimes in a quarter of an hour. 



This process has been described as the method of CHRSCHT- 

 suHONOWtc (Arch. f. mile. Anat., vii, 1872, p. 383). 



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

 the double chloride of gold and potassium has the following- 

 advantages over the simple gold chloride. It is more easy 

 to be obtained of unvarying composition, it is more per- 

 fectly neutral, and its solutions are more perfectly stable. 

 He uses it in solutions of the same strength as chloride of 

 gold, viz. 0'5 per cent. In order to demonstrate the intra- 

 epithelial ramifications of nerves of the cornea, the gold is 

 partially reduced by exposure of the tissue, after impregna- 

 tion for sixteen to twenty-four hours in (one or two ounces 

 of) distilled water, and there are added to the water one or 

 two drops of a pyrogallic acid developing solution, such as 

 is used in photography (vide G-EKLACH, Die Photographic als 

 Hiilfsmittel der mikrosltopischen Forsvhnng, Leipzig, 1863). 

 Or instead of treating them with the developing solution, the 

 cornea may be removed to a warm concentrated solution of 

 tartaric acid, and remain there at the temperature of an in- 

 cubating stove until the gold is fully reduced. 



I have myself used the double chloride of gold and sodium 

 with good results. 



CIACCIO (Joimi. de Microgr., vii, 1883, p. 38; Journ. Boy. 

 Mic. Soc. [N.S.],iii, 1883, p. 290) prefers the double chloride 

 of gold and cadmium. 



