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. In training, soldiers were required to hold their breath for six seconds while the mask was being adjusted. It was explained to them that four breaths of the deadly chlorine gas was sufficient to kill; the first breath produced a spasm of the glottis; the second brought mental confusion and delirium; the third produced unconsciousness; and the fourth, death. The bag containing the gas mask and respirator was carried always by the soldier. The soldier during the winter season in the front line trenches was a grotesque figure. His head was crowned with a helmet covered with khaki because the glint of steel would advertise his whereabouts. Beneath the helmet he wore a close fitting woolen cap pulled down tightly around his ears and sometimes tied or buttoned beneath his chin. Suspended upon his chest was the khaki bag containing gas mask and respirator. Over his outer garments were his belt, brace straps, bayonet and ammunition pouches. His rifle was slung upon his shoulder with the foot of a woolen sock covering the muzzle and the leg of the same sock wrapped around the breech. A large jerkin made of leather, without sleeves, was worn over the short coat. Long rubber boots reaching to the hips and strapped at ankle and hip completely covered his legs. When anticipating trench raids, or on a raiding party, a handy trench knife and carefully slung grenades were added to his equipment. Airplane bombing ultimately changed the whole character of the war. It extended the fighting lines miles behind the battle front. It brought the horrors of night attacks upon troops resting in billets. It visited destruction and death upon the civilian population of cities scores of miles back of the actual front. Germany transgressed repeatedly the laws of humanity by bombing hospitals far behind the battle front. Describing one of these atrocious attacks, which took place May 29, 1918, Colonel G. H. Andrews, chaplain of a Canadian regiment, said: "The building bombed was one of three large Red Cross hospitals at Boulenes and was filled with Allied wounded. A hospital in which were a number of wounded German prisoners stood not very far away. "The Germans could not possibly have mistaken the building they bombed for anything else but a hospital. There were flags with a red cross flying, and lights were turned on them so that they would show prominently. And the windows were brilliantly lighted. Those inside heard the buzz of the advancing airplanes, but did not give them a thought.