Gas was invented as a terror weapon meant to instill confusion and panic among the enemy prior to an offensive. It was a sort of physiological weapon with the non-lethal tearing agents inflicting as much panic as the dreaded mustard gas. Mustard gas causes severe blistering even in small quantities. It highly irritates the eyes and quickly causes conjunctivitis and blindness. If mustard gas is inhaled it attacks the respiratory tract and lungs, causing pulmonary edema. Some effects of exposure to mustard gas are delayed up to 12 hr and death may result several days or years after exposure. Mustard gas was introduced by the Germans in warfare against the British at Ypres, Belgium, in July, 1917, and took a heavy toll of casualties. It is dispersed as an aerosol by a bursting shell.