METALLIC STAINS (IMPREGNATION METHODS). 251 



that have been subjected to a special treatment by organic 

 acids ; the other, concerned chiefly with the study of nerve- 

 centres, is characterised by the employment of fixed and 

 hardened tissues. 



These two groups of methods may be distinguished with 

 APATHY as the Foregilding methods (Vorvergoldung), and the 

 Afteryildint) methods (Nachvergoldung). Amongst the latter 

 is one at least, that of APATHY, which affords not only a stain 

 of nervous tissue, but also an excellent nuclear and plasmatic 

 stain of tissues in general. 



A. Fore-gilding. 



349. The State of the Tissues to be impregnated. The once 

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

 should be taken pei'fectly fresh, seems not to be valid for all 

 cases. For DIJASCH (Sitzb. /,-. /,. Aka<L TTV**. Wien, 1881, 

 p. 171, and 1884, p. ~>1(> ; and Aliliaud. math.-pliys. ('I. J. K. 

 Xarli. (le*. (1. IT/'**., xiv, No. 5, 1887; Zeif. f. ivixx. Mil:., iv, 

 4, 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. He 

 eveii suspects that the function of the organic acids in the 

 methods inspired by LOWIT'S method is to bring the tissues 

 into somewhat the state in which they are naturally found at 

 a certain moment of post-mortem process a state, namely, 

 in which the nerves have a special susceptibility for impreg- 

 nation with gold. 



350. COHNHEIM'S Method (Yin-how's Arch., Bd. xxxviii, 

 pp. 346349 ; Strieker'* Huiulb., p. 1100). This, the arche- 

 type of the gold methods, was as follows : Fresh pieces of 

 cornea (or other tissue) are put into solution of chloride of 

 gold of O'o per cent, strength until they are 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. 



The method in this, its primitive form, often gave splendid 

 results, but was very uncertain, giving sometimes a nuclear 



