60 Microscopic Histochemistry 



cial brand of fuchsin. There is nothing in the gross appear- 

 ance of the reagent to indicate spoilage; this manifests itself 

 only by unsatisfactory staining results. Entirely colorless, 

 clear solutions may have lost all their staining power; grossly 

 turbid or pinkish solutions, after filtration or the addition of 

 some more bisulfite for decolorization, may work well. It is 

 always advisable to keep a few slides, known to contain gly- 

 cogen or mucin, handy and perform a test run before the 

 main experiment. 



Wermel's solution, although more complicated to prepare 

 than the simple Schiff's reagent, is distinctly more stable 

 than the latter. 



5. The silver sohition.— Either of the following two solu- 

 tions can be used: 



A) Fontanas^^ silver solution.— To a 2-3 per cent solution 

 of silver nitrate add, drop by drop and under continuous 

 shaking, strong ammonia water until the initial brown-gray 

 precipitate dissolves. To the clear mixture add some more 

 silver solution, drop by drop and under continuous shaking. 

 The turbidity resulting from the first few drops will disap- 

 pear easily; continue to add silver solution until a minimal 

 opalescence persists. The solution will keep in the refriger- 

 ator for a few days. 



B) Methenamine-silver stock solution. ^^— Add 5 ml. of a 

 5 per cent AgNOs solution to 100 ml. of a 3 per cent methen- 

 amine solution, shake until the initial heavy white precipi- 

 tate disappears. This mixture will keep in the refrigerator for 

 many months. 



Fontana's solution has a tendency to produce a fine dust- 

 like precipitate all over the slide and a fairly intense back- 

 ground staining. Methenamine-silver is practically free from 

 these drawbacks; the pictures obtained with its use are very 

 clear. 



30. Fontana, A.: Dermat. Ztschr., 46:291, 1925-26. 



