"The officer before us is instructing his squad in the use of gas masks. Thorough drill in this is of the utmost importance, for a few seconds delay in adjusting his mask in a gas attack may incapacitate a soldier for service and subject him in weeks of agony, if not death. The Germans were the first to sue poison gas in the war, expelling it from metal tubes and trusting to the wind to carry it down upon out allies. This method was soon discarded in favor of gas shells, which they used extensively, sometimes one shell in every three being filled with gas. It became necessary to equip every man in our army with a mask and drill him in the use of it. These masks fit so closely that air cannot enter the nostrils except through the breathing tube. The general principle on which they are constructed is this- that the inhaled air is drawn through certain substances which absorb the gas before it can get into the mask, while the breath which a soldier exhales escapes from the mask through a rubber valve opening only on pressure from the inside. The mask is carried in a canvas case, ready for instant use. A soldier, expert in the use of his mask, can put it on in about ten seconds. Soldiers do not like to wear the mask and will often take great risks rather than be annoyed with them, for even the best of them add somewhat to the difficulty of breathing. Then too, moisture which accumulates inside the masks dims the eye glasses and it becomes difficult to see. Throughout the war there was constant effort to produce a gas against which no mask would be effective. The Germans use phosgene, mustard gas, lachrymal gas and others, but our chemists devised masks effective against each."--Taken from back of resource