The use of poison gas, the word being used in its broad sense, is now general. It was first used by the Germans, but as in the case of flame-throwers, the Allies soon gained the ascendency. The first use of asphyxiating gas was by the Germans during the first battle of Ypres. There the deadly compound was mixed in huge reservoirs back of the German lines. From these extended a system of pipes with vents pointed toward the British and Canadian lines. Waiting until air currents were moving steadily westward, the Germans opened the stop-cocks shortly after midnight and the poisonous fumes swept slowly, relentlessly forward in a greenish cloud that moved close to the earth. The result of that fiendish and cowardly act was that thousands of men died in horrible agony without a chance for their lives. Besides that first asphyxiating gas, there soon developed others even more deadly. The base of most of these was chlorine. Then came the lachrymatory or “tear-compelling” gases, calculated to produce temporary or permanent blindness. Another German “triumph” was mustard gas. This is spread in gas shells, as are all the modern gasses. The Germans abandoned the cumbersome gas-distributing system after the invention of the gas shell. These make a peculiar gobbling sound as they rush overhead. They explode with a very slight noise and scatter their contents broadcast. The liquids carried by them are usually of the sort that decompose rapidly when exposed to the air and give off the acrid gases dreaded by the soldiers. They are directed against the artillery as well as against intrenched troops. Every command, no matter how small, has its warning signal in the shape of a gong or a siren warning of approaching gas. Gas masks were speedily discovered to offset the dangers of poison gases of all kinds. These were worn not only by troops in the field, but by artillery horses, pack mules, liaison dogs, and by the civilian inhabitants in back of the battle lines. Where used quickly and in accordance with instructions, these masks were a complete protection against attacks by gas. The perfected gas masks used by both sides contained a chamber filled with a specially prepared charcoal. Peach pits were collected by the millions in all the belligerent countries to make this charcoal, and other vegetable substances of similar density were also used. Anti-gas chemicals were mixed with the charcoal. The wearer of the mask breathed entirely through the mouth, gripping a rubber mouthpiece while his nose was pinched shut by a clamp attached to the mask.