202 METALLIC STAINS 



must be stretched like a drum-head over a porcelain dish, and 

 vcashed first with distilled water, and then washed with a solution 

 of silver nitrate. In order to obtain a powerful stain it is necessary 

 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 

 begun to turn a blackish grey the membrane is removed, washed 

 in distilled water, and mounted on a slide in some suitable examina- 

 tion 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, are quite invisible. 



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 ^v'lth fresh tissues, 



391. Silver Nitrate : the Solutions to be employed (Ranvier). 

 The solutions generally employed by Ranvier vary in strength 

 from 1 : 300 to 1 : 500. Thus 1 : 300 is used for the epiploon, 

 pulmonary endotheliimi, 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 Lymjihgefasse, etc., Berlin, 1862, p. 5). 



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

 varying between 0-1 and 0-2 per cent., which he allowed to act for 

 thirty seconds. 



RouGET {Arch, de Physiol., 1873, p. 603) employed solutions 

 as weak as 1 : 750, or even 1 : 1000, exposing the tissues to their 

 action several times over, and washing them with water after 

 each bath. 



