80 PRACTICAL HISTOLOGY. 



the limbs, this is disarticulated at the proximal joint, 

 and is rinsed for a second or two in a beaker of dis- 

 tilled water, in order to wash away any blood or 

 lymph, which might happen to be on the surface, 

 and which would cause a granular precipitate with 

 the nitrate of silver solution The latter, a solution 

 of 1 part of the salt to 200 of distilled water, is 

 then either poured over the surface or dropped on it 

 from a pipette. After two or three minutes the 

 silver solution is quickly washed off by a stream of 

 distilled water, and the limb is then at once placed 

 in a beaker of spirit, and exposed to direct sunlight, 

 or, failing this, to bright diffused daylight. In a 

 few minutes in the sunlight, and after a longer time 

 in diffused daylight, the silvered surface will have 

 acquired a uniform brownish tinge to the naked eye. 

 When the color is strongly marked, it is as well to 

 remove the beaker from the light, lest the prepara- 

 tion become too darkly stained. The limb should 

 be allowed to remain in the spirit twenty-four hours; 

 at the expiration of this time it is placed in a dish, 

 and, by the aid of fine forceps and scissors, a piece 

 of the superficial stained layer is dissected off under 

 spirit. In doing this, care must be taken not to 

 drag at all upon the membrane which is removed, 

 so as to throw it into creases. The piece is then 

 transferred to water, and floated on to a clean glass 

 slide w r ith the browned surface of the membrane 

 uppermost. The slide is then carefully removed 

 from the water, the portion of tissue being kept flat 

 on its upper surface ; and most of the superfluous 

 water having been wiped away, a cover-glass, on 

 which a drop of glycerine has been placed, is in- 

 verted over the preparation. Before putting on the 

 cover-glass it is well to examine the object under 

 a low power, in order to make sure of the absence 

 of folds and creases or specks of dust upon it : if 

 any such be seen they must be carefully removed 

 with a needle. Indeed, it may be recommended as 

 a golden rule in making histological preparations 



