LOWIT'S METHOD. 145 



endings the tissues should be taken perfectly fresh, seems not 

 to be valid for all cases. For DRASCH (Sitzb. &. k. Acad. 

 Wiss. Wien, 1881, p. 171, and 1884, p. 516; and Abhand. 

 math.-phys. Cl. d. K. Sack. Ges. d. Wiss., xiv, No. 5, 1887 ; 

 Zeit.f. wiss. Mik., iv, 4, 1887, p. 492) finds that better results 

 are obtained with tissue that have been allowed to lie after 

 death for twelve, twenty-four, or even forty-eight hours in a 

 cool place. He even 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 

 impregnation with gold. 



223. 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. 



224. Lowit'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 reduc- 

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



Small pieces of fresh skin are put into dilute formic acid 



10 



