Furthermore, if the need for such training can be avoided it is of course highly desirable. This applies to the mouthpiece of the British respirator; to elastics that cause undue discomfort to the face; to the noseclip and to the large boxes that cause too great resistance to breathing. It may be taken as a general rule that when protection requires so much effort or becomes so much of a burden that the average man cannot or will not endure it, it is high time to find out what the average man will stand and then provide it even if some casualties result. Protection in battle is always relative. A man who cannot balance protection against legitimate risk has no business passing on arms, equipment or tactics to be used in battle. TRAINING Bitter experience taught the Allies as well as the Americans that no matter how efficient the gas mask and other defensive appliances, they would not take the place of thorough and constant training. One of the greatest difficulties at first was to get American troops to realize that a thing as invisible as gas, with in many cases no offensive smell and producing no immediate discomfort, could be deadly. Nothing but constant drill and constant reiteration of these dangers could get this fact impressed on them. Indeed it never was impressed sufficiently in any of the earlier divisions of American troops in the line to prevent their taking such chances that each division suffered heavy loss on one or more occasions from gas attacks. A great deal of emphasis had been placed by the English upon the adjustment of the mask in the shortest possible time, this time having been officially set at six seconds after the alarm. The Americans in adopting the mask _in toto_ naturally had to adopt the rules for adjusting it and wearing it. Experience, however, taught them in a few months that the effort to attain too great speed was dangerous. It tended to rattle the soldier and to result in poor adjustment of the mask, both of which led to casualties. Accordingly in the latest instructions for defense against gas all reference to six seconds was eliminated and emphasis placed on the necessity of accurate adjustment of the mask. Inasmuch as any man, practically without effort or previous drill, can hold his breath for twenty seconds, the need for great speed in adjusting the mask is not apparent. HOLDING THE BREATH The first regulations and those in general use up to near the close of hostilities, prescribed that the soldier should hold his breath and adjust his mask. It seemed impossible to overcome the natural inference that “holding the breath” meant first the drawing of a full breath. This was obviously highly dangerous if gas were actually present before the alarm was heard, as was often the case with projector and artillery gas shell attacks. The change was then made to the phrase “Stop Breathing and Stay Stopped until the Mask is Carefully and Accurately Adjusted.” PSYCHOLOGY IN TRAINING