204 METALLIC STAINS (IMPREGNATION METHODS). 



APATHY (Mitth. Zool Stat. Neapel, xii, 1897, p. 722) formerly 

 employed the aurum chlomtum flavum, but now prefers ihefuscum. 



A. Pre-impregnation. 



362. The State of the Tissues to be Impregnated. The once 

 classical rule, that for researches on nerve-endings the tissues should 

 be taken perfectly fresh, seems not to be valid for all cases. For 

 DRASCH (Sitzb. Akad. Wiss. Wien, 1881, p. 171, and 1884, p. 516 ; 

 and Abhand. maih.-phys. Cl. K: Sach. Ges. Wiss., xiv, No. 5, 1887 ; 

 Zeit. wiss. Mik., iv, 1887, p. 492) finds that better results are obtained 

 with tissues that have been allowed to lie after death for twelve, 

 twenty-four, or even forty-eight hours in a cool place. 



363. COHNHEIM'S Method (Virchow's Arch., Bd. xxxviii, pp. 346 

 349; Strieker" sHandb., p. 1100). Fresh pieces of cornea (or other tissue) 

 are put into 0-5 per cent, solution of chloride of gold until thoroughly 

 yellow, and then exposed to the light in water acidulated with acetic 

 acid until the gold is thoroughly reduced, which happens in the course 

 of a few days at latest. They are then mounted in acidulated glycerin. 



Results very uncertain and anything but permanent. 



364. LOWIT'S Method (Sitzgsber. Akad. Wien, Bd. bad, 1875, 

 p. 1). The following directions are from FISCHER'S paper on the 

 corpuscles of Meissner (Arch. mik. Anat., xii, 1875, p. 366). 



Small pieces of fresh skin are put into dilute formic acid (1 volume 

 of water to 1 of the acid of 1-12 sp. gr.), and remain there until 

 the epidermis peels off. They then are put for fifteen minutes into 

 gold chloride solution (1J to 1 per cent.), then for twenty-four hours 

 into dilute formic acid (1 part of the acid to 1 3 of water), and then 

 for twenty-four hours into undiluted formic acid. (Both of these 

 stages are gone through in the dark.) Sections are then made and 

 mounted in dammar or glycerin. Successful preparations show the 

 nerves alone stained. 



365. RANVIER'S Formic Acid Method (Quart. Journ. Mic. Sci. 

 [N.S.], Ixxx, 1880, p. 456). The tissues are placed in a mixture of 

 chloride of gold and formic acid (4 parts of 1 per cent, gold chloride 

 to 1 part of formic acid) which has been boiled and allowed to cool 

 (RANVIER'S Traite, p. 826). They remain in this until thoroughly 

 impregnated (muscle twenty minutes, epidermis two to four hours) ; 

 reduction is affected either by daylight in acidulated water, or in the 

 dark in dilute formic acid (1 part of the acid to 4 parts of water). 



366. RANVIER'S Lemon-juice Method (Traite, p. 813). RANVIER 

 finds that of all acids lemon juice is the least hurtful to nerve- 



