Until 1915 the soldier’s business was to push or throw pieces of metal at the enemy. Various devices had been employed for throwing them fast or far, and some of them threw other pieces on arrival at their destination, thanks, in the main, to the genius of the unforgotten Major-General Shrapnel. It is true that early in the eighth century A.D. the appropriately named Syrian Callinicus had prolonged the life of the Eastern Roman Empire for another 750 years and saved a large part of Christendom from Mahommedan domination by his invention of “Greek fire,” an inflammable liquid which was, however, later superseded by gunpowder. In the fifteenth century the defenders of Belgrade against the Turks had hit upon a similar device, under the direct inspiration, it was claimed, of the Holy Ghost, but these weapons had fallen into desuetude, their effect being largely psychological. Chemical warfare had been so far foreseen by statesmen that in 1907 the signatories of the Hague Conference agreed to renounce the use of projectiles the sole object of which was the diffusion of asphyxiating or harmful gases. They were thus debarred from using lachrymatory gas, the most humane weapon ever invented; but permitted to discharge gas from cylinders on the ground, an exceedingly cruel practice. This regulation was well meant, but the path to August, 1914, was paved with good intentions. In 1914 none of the great powers had made any preparation for poison-gas warfare, and it was not till April 22nd, 1915, more than eight months after the beginning of the war, that the Germans began its use. During the war, twenty-five different poisonous weapons were employed. Of these only three are gases at ordinary temperatures, and can be discharged from cylinders in which they are stored under pressure. The remainder are liquids which gradually evaporate, yielding a poisonous vapour, or solids which are poisonous in the form of smoke. These poisonous substances so far used fall into four classes according to their effect on men. First come gases and vapours which are poisonous when breathed, but have no effect on the skin, and affect the eyes or nose only when present in concentrations which are poisonous to the lungs. They can all be kept out by respirators, and were of military value only against unprotected troops, or in local surprise-action. This group, which included chlorine and phosgene, are probably almost as obsolete as muzzle-loading cannon. A second group are poisonous only in very high concentrations, but irritate the eyes when present in amounts so small that one part in five million may render a man blind with weeping in a few seconds. There is no evidence, so far as I know, that anyone was killed or even permanently blinded by these substances; but they had a great momentary effect. They can be kept out by respirators, or even goggles.