METALLIC STAINS (IMPREGNATION METHODS). 215 



in distilled water, and viounted 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. 



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 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. In general in a good " impregnation " 

 the contents of the cells, and especially nuclei, ai-e quite in- 

 visible. 



The tissues should be constantly agitated in the silver- 

 bath in order to avoid the formation on their surfaces of 

 deposits of chlorides and albuminates of silver. 



These impregnations only succeed with fresh tissues. 



352. Silver Nitrate : the Solutions to be employed (Eanviee). 

 — The solutions generally employed by Eanvier vary in 

 strength from 1 : 300 to 1 : 500. Thus 1 : SOO is used for the 

 epiploon, pulmonary endothelium, cartilage, tendon; whilst 

 a strength of 1 . 500 is employed for the phrenic centre, and 

 the epithelium of the intestine. For the endothelium of 

 blood-vessels (by injection) solutions of 1 : 500 to 1 : 800 

 are taken. 



M. Duval {Precis, p. 229) takes solutions of 1, 2, or at 

 most 3 per cent. 



V. Recklinghausen used, for the cornea, a strength of from 

 1 : 400 to 1 : 500 [Die Lymphgefasse, etc., Berlin^ 1862, p. 5). 



EoBiNSKi {Arch, de Physiol., 1869, p. 451) used solutions 

 varying between O'l and 0'2 per cent,, which he allowed to 

 act for thirty seconds. 



