Blister Agents - These agents affect the eyes and lungs and blister the skin. During World War I mustard was the only blister agent in major use. It was recognized by a distinctive odor and had a fairly long duration of effectiveness under norma weather conditions. Since the, blister agents have been developed which are odorless and vary in duration of effectiveness. Most blister agents are insidious: there is little or no pain at the time of exposure except with lewisite (L) and phosgene oxime (CX) which cause immediate pain on contact. The development of casualty is somewhat delayed. CX produces a wheal (similar to a bee sting) rather that a water blister which the other blister agents produce. Protection from blister agents is extremely difficult.

• Arsenicals - The arsenicals are a group of related compounds in which arsenic is the central atom. Included in the arsenicals are Lewinstein mustard (H), distilled mustard (HD), lewisite (L), mustard-lewisite mixture (HL), phenildichloroarsine (PD), ethyldichloroarsine (ED), and methyldichloroarsine (MD).
Physiological Action - Mustard acts first a a cell irritant and finally as a cell poison on all tissue surfaces contacted. The first symptoms of HD poisoning usually appear in 4 to 6 hours; the higher the concentration, the shorter the interval of time from the exposure to the first symptoms. The physiological action of HD may be classified as local and systemic. The local action results in conjunctivitis or inflammation of the eyes; erythema (redness of the skin) which may be followed by blistering and ulceration; and inflammation of the nose, throat, trachea, bronchi, and lung tissue. Susceptibility also varies with individuals. Injuries produced by HD heal much more slowly and are more liable to infection than burns of similar intensity produced by physical means or by most other chemicals. Systemic effects of mustard may include malaise, vomiting, and fever, with the time of onset about the same as that of the skin erythema. With amounts approaching the lethal dose, injury to bone marrow, lymph nodes, and spleen may result. Such damage is reflected in the peripheral blood by a drop in the white blood cells. Because these cells are essential in the body for preventing infections, a significant drop in the white blood cells will cause the mustard casualties to be far more susceptible to local and overwhelming infections that the normal individual.

• Nitrogen Mustard (HN-1) and Nitrogen Mustard (HN-2) - The nitrogen mustards are a group of related compounds that may be considered as derivatives of ammonia. In each of these chemical agents, nitrogen is the central atom. These compounds have also been discussed in open scientific literature because of the discovery that they possess medicinal value.
Physiological Action - Irritates the eyes in quantities which do not significantly damage the skin or respiratory tract, insofar as single exposures are concerned. This irritation appears in a shorter time that that from HD. After mild vapor exposure, there may be no skin lesions. After severe vapor exposures, or after exposure to liquid HN, erythema may appear earlier than in HD exposure. HN, like HD, may cause irritation and itching. Later, blisters may appear in the erythematous ares. The shin lesions are similar to those caused by HD. Effects on the respiratory tract include irritation of the nose and throat, hoarseness progressing to loss of voice, and persistent cough. Fever, labored respiration, and moist rales develop. Bronchial pneumonia may appear after the first 24 hours. Following ingestion or systemic absorption, HN causes inhibition of cell mitosis, resulting in depression of the blood forming mechanism and injury to other tissues. Severe diarrhea, which may be hemorrhagic, occurs. Lesions are most marked in the small intestine and consist of degenerative changes and necrosis in the mucous membranes. Ingestion of 2 to 6 milligrams causes nausea and vomiting.