Amyloid Stains

1. Iodine stain. Immerse the specimen in a solution made up of 1 g of iodine, 2 g of potassium iodide, 1 mL of sulfuric acid, and 100 mL of water. Amyloid will turn blue. The specimen is then washed in tap water. Museum specimens are mounted in liquid paraffin. This technique is said to prevent fading of the stained amyloid; without sulfuric acid, amyloid will turn brown.

Edwards and Edwards (22) suggested that the specimens should not be washed but should be put in 70% alcohol until the differentiation is complete. The specimen is then removed from the jar and the alcohol is allowed to evaporate. Subsequently, the tissue, which should be almost dry, is placed in liquid paraffin until it is completely soaked, which may take 8 wk or more. Liquid petrolatum appears to be the best preservative for iodine-stained amyloid containing tissues.

2. Congo red stain (21). The specimen is fixed in Kaiserling I solution (see above) and subsequently immersed for 1 h in 1% Congo red. It then is transferred to a saturated solution of lithium carbonate for 2 min and differentiated in 80% alcohol. Normal arteries and veins tend to retain their color. The specimen is mounted in Kaiserling III solution (glycerin 300 mL, sodium acetate 100 g, 0.5% formalin solution to a final volume of 1,000 mL; adjust to pH 8.0; if necessary, filter to clear the solution). In this instance, sodium hydrosulfite should not be added before sealing the jar.

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