76 Microscopic Histochemistry 



fixation, the mast cells will stain almost blue-black, with only 

 a slight tinge of red. The shade is probably due, at least in 

 part, to the adsorption of the dye on the lead compound ( tolu- 

 idin blue is adsorbed strongly on various insoluble lead 

 precipitates ) . 



d) Amyloid.— The term "amyloid" was coined by Vir- 

 chow^^ to denote a homogeneous., somewhat translucent sub- 

 stance which is deposited in connective tissue under certain 

 pathologic conditions and is stained somewhat like starch 

 (amylos equals starch) by iodine. 



Chemically, the characteristic component of amyloid ap- 

 pears to be a sulfuric ester of a polysaccharide."^^ 



Depending on their age and other poorly understood fac- 

 tors, the staining reactions of deposits of amyloid are rather 

 variable. Recent deposits may not show some or even any of 

 the typical staining properties, whereas old deposits usually 

 stain according to textbook specifications. 



The two most important tinctorial features of amyloid are 

 its stainability by iodine and its metachromasia. 



The iodine reaction.— This is very similar to that of glyco- 

 gen, with the exception that the mahogany brown shade may 

 turn into a dark gray-bluish or greenish one on the applica- 

 tion of dilute mineral acid. 



Metachromasia of amyloid: Methods 



1. Stain section in a dilute (0.1-0.2 per cent) solution of 

 methyl violet (or crystal violet) for about 10 minutes. Dif- 

 ferentiate in 1 per cent acetic acid until amyloid is purple- 

 red and the background blue. Rinse, mount in glycerin jelly. 

 Preparations not permanent. 



2. This variant yields permanent preparations. Float the 

 parafiin sections directly on the dye solution (warmed to 

 about 37°-45°C.) for about 15-20 minutes. Refloat them on 

 water to wash out excess dye, then on 1-2 per cent acetic 



80. Virchow, R.: Virchows Arch. f. path. Anat., 6:416, 1854. 



