Because it was realized that the slightest flaw or imperfection in a finished mask might well mean the death in agony of an American soldier, an extremely rigid system of inspection was devised. It was discovered, for example, that all thread holes must be filled with gelatine, in order to prevent the gas from being carried through by the thread; that wrinkles in the band around the face and head permitted gas to leak inside the face-piece; that the mouth-piece must be reinforced with bushings so that the soldier would not bite it in the excitement of a gas attack and thereby cut off his own breath. Only the most painstaking and conscientious women—usually those having husbands or sons at the front—were chosen for the work of final inspection, and, even after they had examined each mask in every detail it was again inspected over a bright light in a dark booth for small pinholes which might have escaped the ordinary visual inspection. And, in order to make the inspectors doubly careful, they were frequently required to go into the gas-chambers wearing masks chosen at random from those they themselves had passed. To obtain absolute results as to the protection afforded by a mask, however, breathing tests in a gas-chamber had to be employed. This testing was done by enlisted men of the Gas Defense Division, who spent many hours each day testing masks and canisters in the gas-chambers, sometimes working in a concentration of phosgene as high as 1 per cent. Without hope of glory or promotion, without the lure of decorations, these men day after day, month after month, risked their lives in order that their fellows at the front might have a better chance to live. Though they wore silver instead of gold chevrons, they are as deserving of thanks and admiration as the men who broke the Hindenburg line or battled in the Forest of the Argonne.