Besides this it was necessary to give as many men as possible some idea of the common sense of the operations in which the army was being drilled. This could only be done by giving a clear idea of how the gas is used; how gas travels; where it accumulates; how it can be removed, and so on; and under what conditions a respirator or smoke helmet protects or ceases to protect its wearer. It was on these lines that instruction was built up; and to do it thoroughly it was found that a large number of instructors were required in order to train the officers and noncommissioned officers and to get them to treat their respirators with as great respect as their rifles and to learn to carry them through a gas-defence drill in just as smart a manner as the ordinary arms. For this purpose special schools of instruction were started at each army headquarters, and as many regimental officers and noncommissioned officers as possible were given a four or five days’ course of gas training, so that they in their turn could go back to their regiments and spread the gospel, as the responsibility for getting things done must eventually fall upon them. Not only was it found impossible to provide specialist officers for each regiment or battalion, but it was recognised that such a procedure would have a bad effect on the gas-defence measures. Gas defence was a matter which affected everybody and was in no way to be regarded as a specialist’s job; battalions were already full of specialists. Indeed the colonels were apt to complain that they had nobody but specialists to command. There were bombers, snipers, signalers, machine gunners and sanitary men; and at that time the trench-mortar personnel was also a part of the infantry battalion. With all these things the feeling was that if a job could be looked on as being a specialty it should be put on the specialist officer concerned, and nobody else worried about it much. Now if gas defence was to become Lieutenant Snook’s job, it meant that it was going to be nobody else’s job, and it was essential that the idea should grow up in the army that gas defence was a purely military matter and affected everybody. What was said then is just as true to-day--that the defensive appliance is a certain protection if it is used properly and in time. Defence against gas is thus on an entirely different footing from defence against shells and bullets, where protection cannot be assured; and, to quote instructions on the subject: “For destructive effects gas must depend on surprise, on poor discipline or on defective appliances. Consequently gas casualties are preventable if the soldier is trained continually to exercise vigilance and is well drilled in the use and care of his respirator.”