METALLIC STAINS (IMPREGNATION METHODS). 255 



FLECHSIG (Die Leitungsbahnen in Gehirn, 1876 ; Arch. f. 

 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 

 glycerin (quoted from G-IEKKE'S Farberei z. mik. Zwecken). 



BOHM reduces in PRITC HARD'S solution amyl alcohol , 1 ; 

 formic acid, 1 ; water, 98. 



MANFRED i treats fresh tissues as follows (Arch, per le Set. 

 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. 



BOCCARDI (Lavori Ins tit. Fisiol. Napoli, 1886, i, p. 27 ; 

 Journ. Roy. Hie. 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. Objects should remain in this fluid in the 

 dark not longer than two to four hours. 



KOLOSSOW (Zeit.f. winy. 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 0*01 per cent, to 0*02 per cent, 

 solution of chromic acid. 



GKBERG (Intern. Monatxschr., 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 

 Lo WIT'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 no re- 

 action occurs to test-paper. " 



APATHY (Mikrotechnik, p. 173 ; Mitth. Zool. Stat. Neapel, 

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



