110 METALLIC STAINS. 



for a few minutes in water acidulated with acetic or formic 

 acid. THANHOPPEE (Das Mikroskop., 1880) recommends this 

 method. He employs a 2 per cent, solution of acetic acid. 



KRAUSB brings his preparations, after washing, into a light 

 red solution of permanganate of potash. Reduction takes 

 place very quickly, even in the dark. The method does not 

 always succeed (see G-IEEKE in Zeit. f. wiss. Mik. } i, 1884, 

 p. 400). 



OPPITZ brings his preparations for two or three minutes 

 into a 0*25 or 0*50 per cent, solution of chloride of tin. 

 Reduction takes place very rapidly (GiEEKE, 1. c.). 



JAKIMOVITCH (Journ. de VAnat., xxiii, 1888, p. 142 ; Journ. 

 Roy. Mic. 8oc., 1889, p. 297) brings nerve preparations, as 

 soon as they have become of a dark brown colour, into a 

 mixture of formic acid, one part, amyl alcohol, one part, and 

 water 100 parts. The objects exposed to the light in this 

 mixture for two or three days at first become brighter, a part 

 of the reduced silver being dissolved ; hence the mixture must 

 be renewed from time to time. When all the silver has dis- 

 solved, a darker colour is permanently assumed. The nerve- 

 cells are left in this mixture for five to seven days. 



200a. After-blackening. LEGEOS (Journ. de VAnat. , 1868, 

 p. 275) washes his preparations after reduction in hyposulphite 

 of soda which prevents after-blackening. According to 

 DUVAL (Precis, p. 230) they should be washed for a few 

 seconds only in 2 per cent, solution, and then in distilled 

 water. 



201. The Hoggans' Histological Rings are vulcanite rings 

 made in pairs, of which one ring just fits into the other, so as 

 to clip and stretch pieces of membrane between them. They 

 will be found described and figured in Journ. Roy. Mic. Soc., 

 ii, 1879, p. 357, and in ROBIN'S Journ. de VAnat, 1879, p. 54. 

 They may be obtained, in sets of various sizes (that of seven- 

 eighths of an inch being the most convenient for 3x1 slides) 

 of Burge and Warren, 42, Kirby Street, Hatton Garden, 

 London, E.G., price ten shillings the dozen pairs. 



This useful little apparatus has lately been reinvented by 

 Eternod (Zeit. f. wiss. Mik., iv, 1, 1887, p. 39), and is iniidc 

 according to his designs by Demaurex, l>;m<l;i^isU', Kusterie, 

 Geneva (Switzerland). 



