To meet these local conditions metal shell cases were first hung up and the alarm sounded on them. Later steel triangles were used in the same way. At a still later date the large policeman’s rattle, well known in Europe, was adopted and following that the Klaxon horn. As the warfare of movement developed the portability of alarm apparatus became of prime importance. For those reasons the Klaxon horn and the police rattle were having a race for popularity when the Armistice was signed. A recent gas alarm invention that gives promise is a small siren-like whistle fired into the air like a bomb. It is fitted with a parachute which keeps it from falling too rapidly when the bomb explodes and sets it free. Its tone is said to be very penetrating and to be quite effective over an ample area. Since future gas alarm signals must be efficient and must be portable, the lighter and more compact they can be made the better; hence the desirability of parachute whistles or similar small handy alarms. ISSUING NEW MASKS One of the problems that remained unsolved at the end of the war was how to determine when to issue new boxes, or canisters, for masks. One of the first questions asked by the soldier is how long his mask is good in gas, and how long when worn in drill where there is no gas. This information is of course decidedly important. Obviously, however, it is impossible to tell how long a canister will last in a gas attack, unless the concentration of gas is known—that is, the life of the box is longer or shorter as the concentration of gas is weak or heavy. A realization of this need led mask designers to work very hard, long before the necessity for comfort in a mask was as fully realized as it was at the end of the war, to increase the length of life of the canister. To get longer life they increased the chemicals and this in turn increased the breathing resistance, thereby adding to the discomfort of the soldier when wearing the mask. Finally, however, it was found that in the concentration of gas encountered on an average in the field, the life of the comparatively small American boxes was sufficient to last from fifty to one hundred hours, which is longer than any gas attack or at least gives time to get out of the gassed area. The British early appreciated the necessity of knowing when boxes should be replaced. They accordingly devised the scheme of furnishing with each mask a very small booklet tied to the carrying case in which the soldier could not only enter a complete statement of the time he had worn the mask but also the statement as to whether it was in gas or for drill purposes only. The soldier was then taught that if he had worn the mask, say for forty hours, he should get a new box. But the scheme didn’t work. In fact, it was one of those things which foresight might have shown wouldn’t work. Indeed, any man who in the hell of battle can keep such a record completely, should be at once awarded a Distinguished Service Medal.