148 METALLIC STAINS (IMPREGNATION METHODS). 



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- 

 SCHONOWIC (Arch.f. mik. Anat., vii, 1872, p. 383). 



HOYER (Arch. f. mik. Anat., ix, 1873, p. 222) proceeds as 

 follows : (For corneal nerves.) 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 perfectly neutral, and its solutions are 

 more perfectly stable. It is used in solutions of the same 

 strength as chloride of gold, viz. 0'5 per cent. Corneas 

 must be very thoroughly imbibed with the solution. Small 

 corneas (rabbit, guinea-pig) require half to one hour, human 

 corneas two to five hours (in an acidulated solution). It is 

 better to err on the side of too prolonged immersion rather 

 than the contrary. In order to demonstrate the intra-epithe- 

 lial ramifications of nerves, the gold is partially reduced by 

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

 ounces of) distilled water, and there is added to the water one 

 or two drops of a pyrogallic acid developing solution, such 

 as is used in photography (vide GERLACH, Die Photographie 

 als Hulfsmittel der mikroskopischen Forscliung, Leipzig, 1863). 

 Or instead of treating them with the developing solution, the 

 corneas may be removed to a warm concentrated solution of 

 tartaric acid, and remain there at the temperature of an 

 incubating stove until the gold is fully reduced. 



I have myself used the double chloride of gold and sodium 

 with good results. 



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

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

 of gold and cadmium. 



GERLACH, whose preparations of nerve-centres are said not 

 to have been equalled since, proceeded as follows (Strieker's 

 Handb., 1872, p. 678) : Spinal cord is hardened for fifteen to 

 twenty days in a 1 to 2 per cent, solution of bichromate of 

 ammonia. Thin sections are made and thrown into a solution 

 of 1 part of double chloride of gold and potassium to 10,000 

 parts water, which is very slightly acidulated with HC1. They 

 remain there from ten to twelve hours, and having become 

 slightly violet, are washed in hydrochloric acid of 1 to 2 : 3000 

 strength, then brought for ten minutes into a mixture of 1 



