Cyanides (the principal "blood agent" in chemical warfare) release cyanide ions in the body, and act by inactivating cytochrome oxidase, which prevents the cell from utilizing oxygen. Low doses cause headaches, weakness, disorientation, and nausea. Higher doses are acutely lethal causing circulatory effects, seizures and respiratory and cardiac failure. The mucosal membranes and skin of casualties appear dark red because the cells cannot utilize oxygen.