208 METALLIC STAINS 



HoYER {Arch. mik. Anat., ix, 1873, p. 222) says that the double 

 chloride of gold and j)otassiurn has many advantages over the 

 simple gold chloride. He impregnates in solutions of 0-5 per 

 cent, strength, and reduces in water containing 1 or 2 drops of a 

 pyrogaUic acid developing solution, such as is used in photography, 

 or in a warm concentrated solution of tartaric acid, at the tem- 

 perature of an incubating stove. 



Lee 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 Leitungsbahnen in Gehirn, 1876 ; Arch. Anat. 

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

 soda. 



Nesteroffsky treats impregnated preparations with a drop of 

 a^nmonium sulphide, and finishes the reduction in glycerin (quoted 

 from Gierke's Fdrberei z. mik. Zzvecken). 



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

 acid, 1 ; water, 98. 



Manfredi {Arch, per le Sci. med., v. No. 15) puts fresh tissues 

 into gold chloride, 1 per cent., for half an hour ; then oxalic acid, 

 0-5 i3er cent., in which they are warmed in a water-bath to 36°. 

 Moimt in glycerin. Sunny weather is necessary. 



BoccARDi {Lavori Instit. Fisiol. Napoli, 1886, i, p. 27 ; Journ. 

 Roy. Mic. Soc, 1888, p. 155) recommends oxalic acid of 0-1 per 

 cent, or of 0-25 to 0-3 per cent., or a mixture of 5 c.c. pure formic 

 acid, 1 c.c. of 1 per cent, oxalic acid, and 25 c.c. of water, reducing 

 in the dark not longer than two to four hours. 



KoLossow {Zeit. wiss. Mik., v, 1888, p. 52) impregnates for 

 two or three hours in a 1 per cent, solution of gold chloride acidu- 

 lated with 1 per cent, of HCl, and reduces for two or three days 

 in the dark in a 0-01 per cent, to 0-02 per cent, solution of chromic 

 acid. 



Geberg {Intern. Monatsschr., x, 1893, p. 205) states that 

 previous treatment of tissues for twenty-four hours with lime- 

 water (Arnstein's method) greatly helps the reduction. 



Bernheim {Arch. Anat. Phys., Phys. Abth., 1892, Supp., p. 29) 

 adds to Lowit's dilute formic acid a piece of sulphite of sodium 

 (must be fresh and smell strongly of sulphurous acid). 



Dr. Lindsay Johnson writes that besides the " sunning " of 

 the impregnating solution recommended above (§ 356), the gold 

 should be carefully acidulated zcith a neutral acetate or formate, 

 or acetic or formic acid, at least twenty-four hours before using ; 

 and then afterwards the tissue must be washed until no reaction 

 occurs to test-paper. 



Apathy {Mikrotechnik, p. 173 ; Mitth. Zool. Stat. Neapel, xii, 

 1897, pp. 718 — 728) lays stress on the necessity of having the 



