(nerve poison). One of several toxic chemical warfare agents developed in Germany during World War II. They are organic derivatives of phosphoric acid (principally alkyl phosphates, fluorophosphates, and thiophosphates). They inhibit the enzyme cholinesterase and cause acetylcholine poisoning and cessation of nerve transmission. They are colorless, odorless, tasteless liquids of low volatility and are absorbed rapidly through the eyes, lungs, or skin; they are lethally toxic to higher animals and humans. Many insecticides have the same structure and properties. Antidotes are atropine sulfate and pralidoxime iodide.See Parathion; Cholinesterase Inhibitor.