Gas travels quickly, so you must not lose any time; you generally have about eighteen or twenty seconds in which to adjust your gas helmet. A gas helmet is made of cloth, treated with chemicals. There are two windows, or glass eyes, in it, through which you can see. Inside there is a rubber-covered tube, which goes in the mouth, You breathe through your nose; the gas, passing through the cloth helmet, is neutralized by the action of the chemicals. The foul air is exhaled through the tube in the mouth, this tube being so constructed that it prevents the inhaling of the outside air or gas. One helmet is good for five hours of the strongest gas. Each Tommy carries two of them slung around his shoulder in a waterproof canvas bag. He must wear this bag at all times, even while sleeping. To change a defective helmet, you take out the new one, hold your breath, pull the old one off, placing the new one over your head, tucking in the loose ends under the collar of your tunic. For a minute, pandemonium reigned in our trench,--Tommies adjusting their helmets, bombers running here and there, and men turning out of the dugouts with fixed bayonets, to man the fire step. Reinforcements were pouring out of the communication trenches. Our gun's crew were busy mounting the machine gun on the parapet and bringing up extra ammunition from the dugout. German gas is heavier than air and soon fills the trenches and dugouts, where it has been known to lurk for two or three days, until the air is purified by means of large chemical sprayers. We had to work quickly, as Fritz generally follows the gas with an infantry attack. A company man on our right was too slow in getting on his helmet; he sank to the ground, clutching at his throat, and after a few spasmodic twisting, went West (died). It was horrible to see him die, but we were powerless to help him. In the corner of a traverse, a little, muddy cur dog, one of the company's pets, was lying dead, with his two paws over his nose. It's the animals that suffer the most, the horses, mules, cattle, dogs, cats, and rats, they having no helmets to save them. Tommy does not sympathize with rats in a gas attack. At times, gas has been known to travel, with dire results, fifteen miles behind the lines. A gas, or smoke helmet, as it is called, at the best is a vile-smelling thing, and it is not long before one gets a violent headache from wearing it. Our eighteen-pounders were bursting in No Man's Land, in an effort, by the artillery, to disperse the gas clouds. The fire step was lined with crouching men, bayonets fixed, and bombs near at hand to repel the expected attack. Our artillery had put a barrage of curtain fire on the German lines, to try and break up their attack and keep back reinforcements. I trained my machine gun on their trench and its bullets were raking the parapet.