The question of smokes is more serious. It was the hope of the producers of irritant smokes that they would penetrate the gas-masks in sufficient amounts to cause sneezing and force their victims to remove their masks, thus exposing themselves to greater concentrations of smoke and to poisonous vapours liberated along with the smoke. This was the German view when they introduced the “Blue Cross” shell in July, 1917. Fortunately, by that time our defence against gas and smoke was extremely good, and we had foreseen the smoke menace and introduced, between April and June, 1917, a filter which effectively stopped it in the concentrations then met in the field. It is not, however, at all unlikely that concentrations of smoke will be produced in the future which will penetrate our present masks. If our anti-gas measures are sufficiently neglected the consequences may, of course, be very serious. It would seem likely that the chemical weapons of the future will not be so very unlike those of the past. The main efforts of the soldier who uses them will be devoted, first, to blistering his enemy, secondly, to tiring him out by forcing him to wear a respirator continuously, which, of course, enormously hampers him for doing anything else. In the Great War mustard gas and sensory irritant smokes were not used as the principal weapons of attack or defence, because the smokes would not incapacitate everyone in a given area, though they would make them keep their respirators on. Mustard gas, on the other hand, could make any area absolutely untenable by the defenders, but the vapour persisted for so many days that it could not be occupied by the attackers either. It was mainly used to produce casualties a few days or weeks before an attack on the units which would be defending, and to protect the flank of an offensive against counter-attack. Thus in April, 1918, Armentières, the original Northern limit of the German attack in Flanders, was so heavily shelled with “mustard” that the gutters in the streets were reported to be running with it. The Germans themselves received orders forbidding them to enter its ruins for a fortnight. Nevertheless, mustard gas is so adequate a weapon that the attempt will almost certainly be made to use it not merely for making ground untenable for both sides, but for gaining it from the enemy. For this purpose the following methods suggest themselves. First, attempts might be made to protect troops completely from the effect of gas on their skins by encasing them in airtight overalls and gloves. These were used with a certain amount of success by machine-gunners in the Great War, but would hardly be practicable for attackers, who would, except perhaps in winter, die of heat-stroke if encased in such apparatus.