SILVER NITRATE. 137 



into the fibrous tissue, on the surface of which it is reduced 

 by the action of light. The cells of the tissues will be found 

 unstained. 



Silver nitrate is generally employed in solution in the fol- 

 lowing manner : A 1 per cent, solution is taken, to which 

 two, three, or four volumes of water are added according to 

 circumstances. The mode of employment varies in its details 

 according to circumstances, a point which is very important 

 to observe. In the case of a membrane such as the epiploon, 

 the membrane must be stretched like a drum-head over a 

 porcelain dish,* and washed with distilled water, in order to 

 remove the albuminates and white blood-corpuscles that are 

 found on its surface ; it is then washed with the solution of 

 silver nitrate. In order to obtain a powerful stain it is neces- 

 sary that this part of the operation be performed in direct 

 sunlight, or at least in a very brilliant light. As soon as the 

 tissue has become white, and has begun to turn of a blackish 

 grey, the membrane is removed, washed in distilled water, 

 and mounted on a slide in some suitable examination 

 medium. 



If the membrane were left in the water the cells would 

 become detached, and would not be found in the finished 

 preparation. 



If the membrane had not been stretched as directed the 

 silver would be precipitated not only in the intercellular 

 spaces, but in all the small folds of the surface, and the forms 

 of the cells would be disguised. 



If the membrane had not been washed with distilled water 

 before impregnation there would have been formed a deposit 

 of silver on every spot on which a portion of an albuminate 

 was present, and these deposits might easily be mistaken for 

 a normal structure of the tissue. It is thus that very often 

 impurities in the specimen have been described as stomata of 

 the tissue. 



If the solution be taken too weak for instance, 1*500 or 

 1*1000, or if the light be not brilliant a general instead of an 

 interstitial stain will result ; nuclei will be most stained, then 

 protoplasm, and the intercellular substance will contain but 

 very little silver. 



* The Hoggans' histological rings, for which see below, 216, will be 

 found much more convenient. 



