The scene is a base camp behind the Western Front. In the background is a gravel pit, its brow fringed with pines. On the right-hand side is a black hut; against one wall several cast-iron cylinders are leaning; against another several stretchers; behind it a squad of R.A.M.C. orderlies are playing pitch and toss for profit and pleasure. On the left-hand side is a cemetery.  
On the turf in the centre of the stage are some two hundred members of the well-known British family, Atkins. The matter in hand being merely that of life and death those in the rear ranks are whiling away the time by playing crown and anchor. Their less fortunate comrades in the prominence of the front ranks are "havin' a bit o' shut eye"—in other words are fast asleep sitting up, propped the one against the other.
 
Before them stands a Bachelor of Science disguised as a Second Lieutenant. From the green and black brassard about his arm and the attar de chlorine and parfum de phosgene which cling about him in a murky aureole one would guess him to be connected with the Gas Service. And one would be quite correct; he is.
 
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Lecturer: "Ahem! Pay attention to me, please; I am going to give you a little chat on Gas. When you go up the line one of two things must inevitably happen to you; you will either be gassed or you will not. If you are not gassed strict attention to this lecture will enable you to talk as if you had been. On the other hand, if you are gassed it will enable you to distinguish to which variety you succumbed, which will be most instructive.
 
"There are more sorts of gas than one. There is the Home or Domestic Gas, which does odd jobs about the house at a bob a time, and which out here is fed to observation balloons to get them off the earth. There is Laughing Gas, so called from the fun the dentist gets out of his victims while they are under its influence; and lastly there is Hun Gas, which is not so amusing.
 
"Three varieties of gas are principally employed by the Hun. The first of these is Chlorine. Chlorine smells like a strong sanitary orderly or weak chloride of lime. The second on our list is Mustard Gas, so called because it smells like garlic. Everything that smells of garlic is not Mustard Gas, however, as a certain British Division which went into the line alongside some of our brave Southern allies regretfully discovered after they had been sweltering in their masks for thirty-six long, long hours.
 
"The third and last is Phosgene. Phosgene has a greenish whitish yellowish odour all its own, reminiscent of decayed vegetation, mouldy hay, old clothes, wet hides, burnt feathers, warm mice, polecats, dead mules, boiled cabbage, stewed prunes, sour grapes, or anything else you dislike.
 
"As all these gases have a depressing effect on the consumer if indulged in too freely the War Office has devised an effective counter-irritant, the scientific wonder of the age, the soldier's friend and multum in parvo—in short, the Respirator-Box. Here you will observe I have a respirator-box as issued to the troops.
 
"There are other kinds with lace trimmings and seasonable mottoes worked in coloured beads for the use of the Staff; but they do not concern us. Let us now examine the ordinary respirator-box. What do we discover? A neat canvas satchel, knapsack or what-not, which will be found invaluable for the storage of personal knick-knacks, such as soap, knives and forks, socks, iron rations, mouth-organs, field-marshal's batons, etc. Within the satchel (what-not or knapsack) we discover a rubber sponge-bag pierced with motor goggles, a clothes-peg, a foot of garden hose, a baby's teether (chewers among you will find this a comforting substitute for gum), a yard or two of strong twine (first-aid to the braces), a tube of Anti-Dimmer (use it as tooth-paste, your smile will beam more brightly), and a record card, on which you are invited to inscribe your name, age, vote and clubs; your golf, polo and ludo handicaps; complaints as to the cooking or service and any sunny sentiments or epigrams that may occur to you from time to time.
 
"Should you be in the line and detect the presence of hostile gas in large numbers your first action should be to don your respirator-box and your second to give the alarm. The donning of the respirat............