Nobody ever needs an antidote unless he has been poisoned. An antidote by itself has no meaning. It is a substance which prevents the action of a poison. And a poison is any substance which produces harmful or deadly effects on living tissue.

There are basically four kinds of poisons, divided according to the way they affect the body. Corrosive poisons (like strong acids) destroy tissues locally. Irritant poisons produce congestion of the organ with which they come in contact. The next kind of poison, neurotoxins, affect the nerves within the cell. And finally, the hemotoxins combine with the blood and prevent oxygen from forming hemoglobin. Carbon monoxide (such as comes from the exhaust of an automobile) is a hemotoxin. It causes death because the blood is deprived of oxygen that nourishes the tissues and brain.