The following four principles were set down in that letter: (_a_) That the mask must give protection and that experience had shown that suitable protection could only be obtained by drawing the air through a box filled with chemicals and charcoal. (_b_) That there must be clear vision and that experience to date indicated that the Tissot method of bringing the inspired air over the eyepieces was by far the best, (_c_) That the mask must be as comfortable as compatible with reasonable protection, and that this meant the mouthpiece and noseclip must be omitted. (_d_) That the mask must be as nearly fool proof as it could be made. That is, it should be of quick and accurate adjustment, in the dark or in the trenches, and be difficult to disarrange or injure once in position. =Gas Training and Battle of Picardy Plains.= On March 21, 1918, as is known to everyone, the Germans began their great drive from Cambrai across the Picardy Plains to Amiens. While the battle was expected it came as a complete surprise so far as the tactics used, and the extent and force of the attack, were concerned. Lieutenant Colonel G. N. Lewis, who had been sent about March 1 to British Gas Schools, and had been assigned to one of the schools run by the Canadians, was thus just on the edge of the attack. This gave him an opportunity to actually observe some of that attack and to learn from eye-witnesses a great deal more. The school, of course, was abandoned hurriedly and the students ordered back to their stations. Lewis submitted two brief reports covering facts bearing on the use of gas and smoke by the Germans. These reports exhibited such a grasp of gas and smoke battle tactics that he was immediately ordered to headquarters as assistant on the Defense side of gas work, that is, on training in gas defense. Up to that time no one had been able to organize the Defensive side of gas work in the way it was felt it must be organized if it were to prove a thorough success. A month later he was put at the head of the Gas Defense Section, and in two months he had put the Defense Division on a sound basis. He was then ordered to the United States to help organize Gas Defense Training there. [Illustration: FIG. 10.—Close Burst of a Gas Shell. The 6th Marines in the Sommediene Sector near Verdun, April 30, 1918.] =Cabled Report on Picardy Battle.= Based partly on Colonel Lewis’s written and oral reports, and also on information contained in Intelligence dispatches and the newspapers, a cablegram of more than 300 words was drafted reciting the main features of the battle so far as they pertained to the use of gas. This cablegram ended with the statement that “the above illustrates the tremendous importance of comfort in a mask” and that “the future mask must omit the mouthpiece and noseclip.”