206 ' METALLIC STAINS 



lised double chloride mixed with an equal weight of chloride of 

 sodium, and contains 25 per cent, of metallic gold," 



This, however, appears not to be the case in Germany. Dr. 

 Grubler, writing to Mayer (see the Grundzuge, Lee und Mayer, 

 p. 215), says : "" Aurum chloratum fuscum contains about 53 per 

 cent. Au, the flavum about 48 per cent. ; in both of them there 

 should be only water and hydrochloric acid besides the gold, no 

 sodium chloride. Pure Auronatrium chloratum contains 14-7 per 

 cent, of sodium chloride, though samples are found in commerce 

 with much more." 



Apathy {Mitth. Zool. Stat. Neapel, xii, 1897, p. 722) formerly 

 employed the aurum chloratum flavum, but now prefers the 

 fuscum. 



A. PRE-IMPREGNATION 



401. 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. iviss. Wien, 1881, p. 171, and 

 1884, p. 516 ; and Ahhand. math.-jjhys. CI. K. Sach. Ges. Wiss., 

 xiv. No. 5, 1887 ; Zeit. iviss. 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. 



402. Cohnheim's Method {Virchow^s Arch., Bd. xxxviii, pp. 346 — 

 349 ; Strieker's Handb., 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. 



403. Lowit's Method {Sitzgsher. Akad. Wien, Bd. Ixxi, 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 dilate 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 (1|^ 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 damar or glycerin. 

 Successful preparations show the nerves alone stained. 



404. 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 jmrt of formic acid) which has been boiled and 



