Another type of shell, known as the "K-shell," contained a very poisonous liquid, the object of which was to destroy the enemy quickly. The effect of this shell was felt at once, but it left no slow vapors on the ground, and so it could be followed up almost immediately by an attack. Later on, the Germans developed three types of gas shell--one known as the "Green Cross," another as the "Yellow Cross," and the third as the "Blue Cross." The Green Cross shell was filled with diphosgene, or a particularly dangerous combination of phosgene in liquid form, which would remain in pools on the ground or soak into the ground and would vaporize when it became warm. Its vapors were deadly. One had always to be on his guard against them. In the morning, when the sun warmed the earth and vapors were seen to rise from the damp soil, tests were made of the vapors to see whether it was mere water vapor or diphosgene, before men were allowed to walk through it. These vapors were heavier than air and would flow down into a trench, filling every nook and cranny. If phosgene entered a trench by a direct hit, the liquid would remain there for days, rendering that part of the trench uninhabitable except by men in gas-masks. The infected part of the trench, however, was cut off from the rest of the trench by means of gas-locks. In other words, blankets were used to keep the gas out, and usually two blankets were hung so that a man in passing from one part of the trench to another could lift up the first blanket, pass under it, and close it carefully behind him before opening the second blanket which led into the portion of the trench that was not infected. The Germans had all sorts of fiendish schemes for increasing the discomfort of the Allies. For instance, to some of their diphosgene shell they added a gas which caused intense vomiting. The Yellow Cross shell was another fiendish invention of the Huns. It was popularly known as "mustard gas" and was intended not to kill but merely to discomfort the enemy. The gas had a peculiar penetrating smell, something like garlic, and its fumes would burn the flesh wherever it was exposed to them, producing great blisters and sores that were most distressing. The material in the shell was a liquid which was very hard to get rid of because it would vaporize so slowly. On account of the persistence of this vapor, lasting as it did for days, these gas shell were usually not fired by the Germans on lines that they expected to attack immediately. THE SNEEZING-SHELL