Each man is trained to put on his mask rapidly. Standing orders compel the man to put on his gas mask immediately the alarm is given or upon his detection of gas by color or odor. Frequent exercises are held to perfect the men in putting on their gas masks rapidly. This drill may be held at the same time as the “stand to” exercises are carried out. The men must have confidence in their gas masks. For this purpose, each man is sent through a “chlorine chamber” several times to give him confidence that, although the gas may be of great density, it has no disagreeable effects. There are also collective protective apparatuses used in dugouts. Each large shelter possesses such apparatus. Besides this, the entrances and openings of each dugout will be closed by a double canvas impregnated with a special chemical solution to neutralize the gas. =Special Precautionary Measures.= First, there is established a system of bells, sirens, and klaxons which are used by the watchers to give the signal of alarm. This signal is taken up and repeated in all parts of the position and to the rear. Careful observation on the part of a garrison may detect signs of a coming gas attack. Metallic noises in the hostile line may indicate the transportation of gas cylinders. Very often the enemy will use little balloons to ascertain the velocity and direction of the wind. Foggy weather is a special time of danger. In each sector or regiment, an officer is in charge of the maintenance of protective gas apparatus and all the measures against gas attack. With the proper precautionary measures and application of the protective measures, the gas attack is not very dangerous. III. Liquid Fire =Protection against Liquid Fire.= The enemy may make an assault with a special detachment of liquid fire operators in the first line. The object of these operators is to throw jets of liquid fire on the occupants of the first line to allow the assaulting columns to penetrate into the position without losses. The only means of combating such an attack is to evacuate the part of the trenches against which the liquid fire is directed, and move by the flanks. Machine guns and automatic rifles should be established to bring flanking fire to bear against the detachment of liquid fire operators. It is impossible to withstand a liquid fire attack if the operators succeed in coming within sixty yards before the garrison can man its parapets. [Illustration] IV. Mines We will consider mines only from the point of view of defense by infantry against them. This consideration will therefore have no relation to mine warfare or the construction of countermines by engineers.