METALLIC STAINS (IMPREGNATION METHODS). 255 



FLECHSIG (Die LeitungsTjahnen in Gehirn, 1876 ; Arch. J. 

 Anat. u. Phys., 1884,, p. 453) reduces in a 10 per cent, solu- 

 tion of caustic soda. 



NESTEKOFFSKY treats impregnated preparations with a drop 

 of sulphydrate of ammonium, and finishes the reduction in 

 g-lycerin (quoted from GIEKKE'S Fdrberei z. mik. Zweckeit). 



BOHM reduces in PRITCHARD'S solution amyl alcohol, 1 ; 

 formic acid, 1 ; water,, 98. 



MANFREDI treats fresh tissues as follows (Arch, per le Sci. 

 med., v, No. 15) : Gold chloride, 1 per cent., half an hour ; 

 oxalic acid, 0'5 per cent., in which they are warmed in a 

 water-bath to 36, allowed to _ cool, and examined. Mount 

 in glycerin. Sunny weather is necessary. 



BOCCAKDI (Lavori Instil. Fixiol. Napoli, 1886, i, p. 27 ; 

 Jonrn. Roy. Mic. Soc., 1888, p. 155) recommends oxalic acid 

 of O'l 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. Objects should remain in this fluid in the 

 dark not longer than two to four hours. 



KOLOSSOW (Zeit.f. ^<.'^s.',. Mik., v, 1, 1888, p. 52) impregnates 

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

 acidulated with 1 per cent, of HC1, 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. 



CTKBERG (Intern. Monatsschr., x, 1893, p. 205) states that 

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

 water (AKNSTEIN'S method) greatly helps the reduction. 



BKRNHEIM (Arch. f. Anat. u. Phys., Phys. Abth., 1892, 

 Supp., p. 29; Zeit.f. wiss. Mik., x, 4, 1893, p. 484) 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 

 ( 336), the following precautions should be taken: "The 

 tissue must be well washed in distilled water, and the gold 

 carefully acidulated with 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 110 re- 

 action occurs to test-paper. " 



APATHY (MiJcrotechnik, p. 173; Mitth. Zoo/. Stat. Neapel, 

 xii, 1897, pp. 718 728) lays stress 011 the necessity of 



