Melzer's reagent

Melzer's Reagent (also known as Melzer's solution) is a chemical reagent used by mycologists to assist with identifying fungus specimens.

It consists of a combination of iodine with chloral hydrate, potassium iodide, and water. One formulation calls for 20 g chloral hydrate; 20 mL distilled water, 0.5 g iodine, and 1.5 g potassium iodide (Miller and Miller, 2006).

Three reactions to Melzer's reagent are possible:
 * tissues turn blue. This is called an amyloid reaction.
 * tissues turn reddish-brown, a dextrinoid reaction.
 * tissues do not change color, or become faintly yellow-brown, a negative reaction.

Among the amyloid rection, two types can be distinguished:
 * tissue turns blue without KOH-pretreatment. This is called euamyloid reaction.
 * tissue turns red in Lugol's solution but shows no reaction in Melzer's reagent; when KOH-pretreated it turns blue in both reagents. This is called hemiamyloid reaction.

Melzer's reagent is toxic to humans due to the chloral hydrate.