Chemical analysis of the blind Green Cross Shell showed the contents to be a colourless liquid known to chemists by the extensive name of “trichlormethylcholoroformate.” Its effects are just as ferocious as the name implies, and experience showed it to be very poisonous. Indeed it is as poisonous as phosgene itself. The Green Cross Shell gas--“diphosgene,” to give it its short name--has many effects and symptoms that make it a dangerous weapon. When dilute it has a peculiar though not particularly nauseating smell, a smell variously described as “earthy,” “mouldy rhubarb”--whatever that smells like--and damp hay. Unlike the shell gases we had encountered before, it has very little effect on the eyes and causes practically no lachrymation. And this was a trap, because we had been used to lachrymators, so that many men despite the obvious smell were not particularly quick in protecting themselves because of the new symptoms. Of course this applies only to such low concentrations as would take a long time to gas a man. In the higher concentrations the Green Cross very quickly asphyxiates--just as phosgene and chlorine do--and there is no question of whether it is deadly or not. The old Army quip about there being only two kinds of people in gas warfare, namely “The Quick and the Dead,” certainly applies if you get a Green Cross Shell bursting close to you. But even for gas shell bursting some distance away immediate and complete protection is necessary because of the delayed or after effects of the gas, which are exactly similar to those of phosgene. Every care that is taken with regard to men poisoned with phosgene has to be taken for men poisoned with Green Cross gas. Those suffering from the effects of the gas are not allowed to exert themselves at all or to take heavy meals. They are kept under close observation for at least two days, and are treated, in fact, as casualties even though they are not apparently ill. Before the need for this was understood an officer I knew was slightly gassed with shell gas but thought nothing of it. Later on he felt a bit queer, and the regimental medical officer advised him to go down to the dressing station. He walked the length of the communication trench and then mounted a “push bicycle” for a mile’s ride to the aid post. The exertion was too much, however, and he reached the aid post only to fall dead.