178 . Silver Impregnation I (chap. 14) 



cases, it is wise not to dissolve completely the precipitate which is first 

 formed; otherwise results can be inferior. 



The use of pyridine, a fat solvent, precedes some methods, removes 

 lecithin, myelin, mitochondria, galactolipids, etc., and makes subse- 

 quent penetration of the silver easier. (This is particularly true for 

 connective tissue.) Toning with gold chloride is optional in many 

 methods, it may yield a more desirable color and may improve contrasts. 

 The timing apparently is variable, actually only long enough to make 

 the desired change in color, usually a few seconds. If the reaction is slow, 

 then the solution has weakened. The final fixing in sodium thiosulfate 

 (Jiypo) is necessary to remove all tmredticed silver. 



It is readily seen by virtue of the many factors involved to make it 

 specific for certain tissue elements, that silver impregnation can be 

 complex. 



Corked bottles should be avoided, since cork extractives may be a 

 disruptive factor resulting in little selective impregnation of tissue 

 elements (Deck and DeSouza, 1959). In all silver methods, take care that 

 metal instrtunents do not come in contact with the silver solution; a 

 black precipitate may dribble down the surface of slides handled in such 

 a manner. Coat forceps with paraffin, or use horn or wooden instru- 

 ments. All glassware for metallic stains (silver, gold, etc.) mtist be acid- 

 clean. Soak in cleaning solution (page 412), wash thoroughly in running 

 water to remove cleaning solution, and rinse 4 or 5 times with distilled 

 water. 



Sections loosening from slides is a common problem during silver 

 impregnations. Davis and Harmon (1949) use a rinse (0.5 ml. of 2% 

 acetic acid, aqueous, in 50.0 ml. of water) before reduction in sulfite and 

 hydroquinone in the Bodian method (page 203). Many technicians find 

 that the Masson gelatine fixative is superior to Mayer's albumen for 

 affixing sections for silver processes. Transferring tmmotnited paraffin 

 sections through all solutions and mounting and deparaffinizing at the 

 conclusion of the method is feasible. 



Smith {1943) warns that ammoniacal silver hydroxide soltitions can 

 become explosive on standing. Several laboratories have experienced 

 explosions when such solutions have been stored for some time; vio- 

 lently explosive silver amide has formed. Prepare ammoniacal silver 

 solutions just before use. 



References: Baker (1958); Beech and Davenport (1933); Bensley (1959); 

 Foot (1929); Kubie and Davidson (1928); Long (1948); and Silver 

 (1942). 



