META.LLLG SL'A.INS (lMPliEGNx\_TION METHODS). 223 



Ma.nfeed[ (Arch, per le 8ai med., v, No. 15) puts fresh 

 tissaes iato gold chloride, 1 pee cent., for half aa hour ; 

 then oxalic acid, 0'5 per cenfc., in •which they are warmed in a 

 water-bath to 36°. Mount in glycerin. Suany weather is 

 necessary. 



BoccARDi {Lavjri Instit. Flsiol. NapoU, 1836, i, p. 27; 

 Journ. Roy. Mic. Soc, 1888, p. 155) recommends o.Kalic acid 

 of O'l per cent, or of 0'2o to 0'3 per cent., or a mixture of 

 5 o.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. Mih., v, 1888, p. 52) impregnates 

 for two or three hours in a 1 per cent, solution of gold 

 chloride acidulated with 1 per cent, of HCl, and reduces for 

 two or three days in the dark in a O'Ol per cent, to 0'02 per 

 cent, solution of chromic acid. 



G-EBERG [Intern. Monatsschr., x, 1893, p. 205) states that 

 previous treatment of tissues for twenty-four hours with 

 lime-ivater (Aenstein'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 to me that besides the " sun- 

 ning" of the impregnating solution recommended above 

 {§ 349), the gold should be carefully acidulated ivitli a 

 neutral acetate or formiate, 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 {MiJcrotechniJc, p. 173; Mitth. Zool. Stat. Neapel, 

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

 having the objects thoroughly penetrated by light from all 

 sides during the process of reduction. Objects, therefore, 

 should always be so thin that light can readily stream 

 through them. He impregnates for a few hours in 1 per 

 cent, gold chloride (§ 361) in the dark, then brings the 

 objects, without washing out with water, the gold solution 

 being just superficially mopped up with blotting-paper, into 

 1 per cent, formic acid. They are to be set up in this, in a 

 tube or otherwise, so that the light may come through them 



