Owing to its non-persistent nature (the odor disappears in from one and a half to two hours) and to its general properties, phosgene really forms an ideal gas to produce casualties. ACTION ON MAN Phosgene acts both as a direct poison and as a strong lung irritant, causing rapid filling of the lungs with liquid. The majority of deaths are ascribed to the filling up of the lungs and consequently to the suffocation of the patients through lack of air. This filling up of the lungs is greatly hastened by exercise. Accordingly, all rules for the treatment of patients gassed with phosgene require that they immediately lie down and remain in that position. They are not even allowed to walk to a dressing station. The necessity of absolute quiet for gassed patients undoubtedly partly accounts for the later habit of carrying out a prolonged bombardment after a heavy phosgene gas attack. The high explosive causes confusion, forcing the men to move about more or less and practically prevents the evacuation of the gassed. In the early days of phosgene the death rate was unduly high because of lack of knowledge of this action of the gas. Due to the decreased lung area for oxygenizing the air, a fearful burden is thrown on the heart, and accordingly, those with a heart at all weak are apt to expire suddenly when exercising after being gassed. As an illustration of the delayed action of phosgene, a large scale raid made by one of the American divisions during its training is highly illuminating. This division decided to make a raid on enemy trenches which were situated on the opposite slope of a hill across a small valley. Up stream from both of the lines of trenches was a French village in the hands of the Germans. When the attack was launched the wind was blowing probably six or seven miles per hour directly down stream from the village, i.e., directly toward the trenches to be attacked. The usual high explosive box barrage was put around the trenches it was intended to capture. Three hundred Americans made the attack. During the attack a little more than three tons of liquid phosgene was thrown into the village in 75- and 155-millimeter shells. The nearest edge of the village shelled with phosgene was less than 700 yards from the nearest attacking troops. None of the troops noticed the smell of phosgene, although the fumes from high explosive were so bad that a few of the men adjusted their respirators. The attack was made about 3 A.M., the men remaining about 45 minutes in the vicinity of the German trenches. The men then returned to their billets, some five or six kilometers back of the line. Soon after arriving there, that is in the neighborhood of 9 A.M., the men began to drop, and it was soon discovered that they were suffering from gas poisoning. Out of the 300 men making the attack 236 were gassed, four or five of whom died.