False alarms are a great nuisance, however, and good arrangements have now been made to prevent their spreading. It is possible to avoid all the unnecessary disturbance to which troops are subjected by a false gas alarm. This disturbance is particularly objectionable in back areas where regiments returned from the trenches are in billets. When the alarm goes everybody has to turn out--probably in the middle of the night. Sentries wake the officers and men in all the billets; messengers have to be sent post-haste to outlying villages or farms with which there is no telephonic communications; respirators are hurriedly inspected and placed in the alert position; the gas-proof curtains of cellars and dugouts are adjusted; the officers move about in the darkness to see that all their men are accounted for and ready; every one is in a state of expectancy--and then the word comes through that it is a false alarm, and the men go back, cursing, to their billets. Not only is an occurrence of this kind wearying to tired troops, but it has the old disadvantage of crying “Wolf, wolf!” when there is no wolf--the consequent determination on the part of the men not to take the next alarm so seriously. Though it was not realised at the time, it is almost certain that the Germans started to use gas in shell almost simultaneously, and probably actually in the first attack, with the use of the poisonous gas clouds in the attacks of April and May, 1915. Many instances came to notice of men’s eyes being strongly affected to such an extent that they could not keep them open. There seemed to be something in the air which made an unprotected man weep copiously if he tried to keep his eyes open, and of course if he closed them he could not see what he was doing. These effects, and a peculiar smell which was noticed both during and after the gas-cloud attacks, gave rise to the belief that something like formaldehyde was being used by the Germans mixed with some chlorine gas. Others described the smell as being that of chloroform or ether, but nobody could say definitely what the material actually was. It was only after a number of blind shell had been obtained and examined that it was realised that the Germans were firing shell filled with liquid which had a powerful lachrymatory effect. It does not appear certain whether the use of lachrymatory liquids for putting men out of action by making their eyes water is in itself contrary to The Hague Convention, as the vapours need not actually be poisonous. This was the case with the first German gas shell, as it was found that the liquid contained consisted only of a material known chemically as “xylyl bromide.” The vapour of this liquid and of many similar substances has a most powerful effect on the eyes, like that of onions but much stronger. Except in very high concentrations it cannot be regarded as poisonous--at any rate not in the sense that chlorine is poisonous.