Of course the soldier has to be practiced in putting the mask on quickly. It is not quite so simple as the old “gas bag,” about which a drill sergeant said to a squad: “You just whops it out and you whops it on.” But it does not take long to make men proficient with the respirator, at any rate on the parade ground. It is making him proficient under conditions of war that counts and all his instruction is now aimed toward this end. With the mask in position and a tin hat on top of his head a soldier has a peculiar beetlelike appearance, which is not very improving, though the following conversation was reported to have been overheard by an officer about to enter a dugout: “’Ere, mate, take yer gas mask off.” “It is off.” “Then for Gawd’s sake put it on!” The Germans were much interested in our new respirators and their development, and apparently had great difficulty in obtaining specimens for examination. During the winter of 1916-17 German soldiers were being offered a reward of ten marks for every British box respirator that they brought in; but as we were doing most of the shooting at that time I can hardly think that Fritz made a fortune out of his chance. But to return to the gas shell. During 1917, it became apparent that the Germans were placing more and more reliance on the use of gas shell and were manufacturing them in enormous numbers. For a whole year after the introduction of the Green Cross there was only one modification of the chemicals used and that was the admixture with the diphosgene of a material which has been called “vomiting gas.” This substance is a chemical named chloropicrin, and it certainly lives up to its pet name if you take a real good breath of it. The boche mixed it with his diphosgene in order to make the latter more potent if possible, or else because he was running short of diphosgene; but he still calls the mixture Green Cross and uses the gas for its killing power. The chief development, however, was rather in the tactics than in the chemicals used. Gas shell were no longer thrown away; each target or area was apparently considered separately and was given enough shell to make certain of putting up a very high concentration of gas on it. At this time the boche divided his gas-shell shoots into two classes--those for “destructive” effect, and those for “harassing” purposes. The destructive fire was intended to take on big targets, which were not only definite but were known to contain living targets--for example, concentration points where troops were bound to be gathered; billeting areas, including well-known villages or towns; areas known to have a number of batteries collected in them, and so on; in the latter case the batteries themselves would be taken on individually if their positions were known.