=Keeping the General Staff Informed of Work.= In the early part of May, 1918, the Americans arrived in the vicinity of Montdidier, south of Amiens, on the most threatened point of the western front. It was on May 18, 1918, that the Americans attacked, took, and held against several counter-attacks the town of Cantigny. Shortly afterward they were very heavily shelled with mustard gas and suffered in one night nearly 900 casualties. Investigation showed that these casualties were due to a number of causes more or less usual, but also to the fact that the men had to wear the mask 12 to 15 hours if they were to escape being gassed. Such long wearing of the British mask with its mouthpiece and noseclip is practically an impossibility and scores became gassed simply through exhaustion and inability to wear the mask. An inspector from General Headquarters in reporting on supplies and equipment in the First Division, stated that one of the most urgent needs was a more comfortable mask. The First Division suggested a mask on the principles of the new French mask which was then becoming known and which omitted the mouthpiece and noseclip. The efforts of the American Gas Service in France to perfect a mask without a mouthpiece and noseclip were so well known and so much appreciated that they did not even call upon the Gas Service for remark. The assistant to the Chief of Staff who drew up the memorandum to the Chief simply said the matter was being attended to by the Gas Service. This illustrates the value of keeping the General Staff thoroughly informed of what is being done to meet the needs of the troops on the firing line. Then, as always, it was urged that a reasonably good mask was far more desirable than the delay necessary to get a more perfect one. Based on these experiences with mask development, the authors are convinced that the whole tendency of workers in general, in laboratories far from the front, is to over-estimate the value of perfect protection based on laboratory standards. It is difficult for laboratory workers to realize that battle conditions always require a compromise between perfection and getting something in time for the battle. It was early evident to the Gas Service in France that we were losing, and would continue to lose, vastly more men through removal of masks of the British type, due to discomfort and exhaustion, than we would from a more comfortable but less perfect mask. In other words when protection becomes so much of a burden that the average man cannot or will not stand it, it is high time to find out what men will stand, and then supply it even at the expense of occasional casualties. Protection in battle is always relative. The only perfect protection is to stay at home on the farm. The man who cannot balance protection against legitimate risks has no business passing on arms, equipment or tactics to be used at the Front.