114 METALLIC STAINS. 



process a state, namely, in which the nerves have a special 

 susceptibility for impregnation with gold. 



206. Cohnheim's Method (Virchow's Arch., Bd. xxxviii, pp. 

 346349; Strieker's Handb., p. 1100). This, the archetype 

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

 (or other tissue to be operated on) are put into solution of 

 chloride of gold of 0*5 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 

 or protoplasmic stain, sometimes an extra-cellular impregna- 

 tion similar to that of nitrate of silver. And the preparations 

 thus obtained are anything but permanent. 



207. Lbwit's Method. The principle of this process is that 

 in order to facilitate the penetration of the gold and its sub- 

 sequent reduction in the tissues, the tissues are made to swell 

 up by treatment with formic acid before being brought into the 

 gold bath, and formic acid is employed to assist the reduction 

 after impregnation. 



The following directions as to this method, which may serve 

 as a type of the modern methods of research on nerve-endings, 

 are taken from FISCHER'S paper on the corpuscles of Meissner 

 (Arch.f. mik. Anat., xii, 1875, p. 366). 



Lowit's method was first published by him in the Wien. 

 Sitzgsber., Ixxi Bd., iii Abth., 1875, p. 1. 



Small pieces of fresh skin are put into dilute formic acid 

 (one volume of water to one 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 per 

 cent, 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.) Thin sections are then 

 made and mounted in dammar or glycerin. Successful prepa- 

 rations show the nerves alone stained, but it is not possible 

 always to control the results. 



