There are various methods of gas attacks such as emanation, cloud or mist, and chemical shells. Emanation is the least important method and consists of scattering chemicals about trenches which are to be deserted. This diem ical when brought in contact with moisture or stirred up by the digging of occuying troops produces a poisonous gas. The cloud or mist method consists of bringing gas up to the front line in cylinders or tanks under heavy pressure and releasing it when the wind is in a favor able direction for carrying it over enemy trenches. On a clear dry day the gas rolls along close to the ground as a faint green mist gradually growing thinner and less deadly as it advances and dissipates. On a damp day the gas, which has a strong affinity for moisture, appears as a greenish yellow cloud bank and is often harmless at as much as 200 yards. Chem ical shells are dangerous because there is no warning. This method is used against the artillery which usually is, too far back to be affected by cloud attacks except under very favorable circumstances. The average shell contains about five pounds of gas in liquid form which expands when released by the explosive charge in about the same ratio as water to steam. A heavy and concentrated attack with these shells produces the same effect as a cloud attack, but with the added element of surprise. Methyl sulphate and pelite are among the most poisonous gases used in shells.
The bromacetone and xylyibromide (used mostly in German shells) are classed as lach rymal gases because they directly affect the lachrymal or tear glands of the eye causing a large secretion of tears and smarting of the eve which temporarily blinds the enemy. The effect of chlorine and bromine depend on the amount of gas in the atmosphere. Both kill by suffrocation when in sufficient quantities. One part of chlorine to one thousand parts of rir will cause paralysis of the glottis and men will tear their throats open with their fingers in their efforts to get air. Bromine effects are identical, but more violent. Phosgene gives a different effect, but the final result is the same. Men attacked by phosgene feel no serious effects for hours, when they suddenly sink into a fatal collapse with all the symptoms of heart failure. The anhydrides, when they come in contact with the moisture of the lungs, like phosgene, form acids corresponding to their bases, with similar effects. The effects of prus sic acid gas are entirely different from the other gases. It acts directly on the nervous system, in dilute form produces dizziness, headache, pains in the chest and difficult breathing, coma and sometimes convulsions preceding the end.
The accepted methods of defense against poisonous gases are the gas mask or helmet and the respirator. Those are of various kinds, but may be divided into two types — the P. H. helmet and the Box respirator. The P. H. helmet consists of a double flannelette bag with two eyepieces and a mouthpiece through which the breath can be exhaled, but which collapses if it is attempted to inhale through it. The flannelette is impregnated with solutions of carbolic acid and phenol, caustic soda, hexamine and glycerine. The carbolic acid and phenol constitute the neutralizing agent for the chlorine gas. The caustic soda is a protection against prussic acid and hexamine takes out the phosgene. Signal stations, command posts, dressing stations and dugouts for troops in the support line when in the zone of gas at tacks are generally provided with blanket cur tains impregnated with these chemicals. The box respirator consists of a small canvas haver sack (called a satchel), of two compartments, one of which contains the metal filter with its charge of chemicals; the other (the mask), called the facepiece, is made of rubberized ma terial with mica eyepieces, a nose clip, a rubber mouthpiece shaped to be gripped in the teeth and terminating on the outside in a flat rubber valve similar to that on the P. H. helmet. The
mask fits the face closely and is held in place by broad elastic bands passing around the head.
The anti-gas horse respirator consists of a flannelette bag with a canvas mouthpiece which goes into the horses mouth and saves the flannelette from being bitten through. The bag is provided with an elastic band which passes round the opening so as to draw the respirator close to the face when in use. In side the bag and attached to the canvas mouth piece there is a canvas frame which is stitched on to the bag in such a way as to prevent the material being drawn into the nostrils when the respirator is in use. The whole is folded and carried in a canvas case provided with a flap. Horses can stand a higher concentration of gas than human beings without serious damage and hence it • is not necessary to protect them against cloud gas attacks when they are a great distance behind the trenches. Nor is it neces sary to protect their eyes. The respirator is primarily intended for use on transport ani mals when they are sent to the trenches with supplies, ammunition, etc. When not required for immediate use the respirator can be con veniently carried on the supporting strap of the breast harness, or if a zinc wither pad is worn, still more conveniently inside this pad. However carried, the case is steadied by being strapped on either side to the metal ring on the supporting strap, and its flap should be passed under this strap, between it and the numnah wither pad, and buttoned as in the alert posi tion. Poisonous gases have been used in war fare with the intention of forcing men out of action, hampering artillery, preventing supports from advancing, and inspiring terror, so that an advance may be made with a slight opposition and some military advantage secured. Apart from a question of an advance, poisonous gases have been used merely as a means of causing casualties on the opposing side and of inspiring general terror.
Rest is the most important point of all in the general treatment of gas casualties. Men, and especially officers, should be warned be forehand that if lightly gassed they must re frain from moving about or calling out orders. Physical strain after gassing may involve the loss of a life that might otherwise have been restored in a brief time. The principle of at taining complete rest as soon as possible under lies the detailed advice for dealing with gas casualties, and is the reason for their detention at the casualty clearing stations. Arrangements should be planned beforehand at each casualty clearing station so that even a large number of gas casualties can be handled with discipline and control. Next in importance to rest comes the use of oxygen, protection from cold, special stimulants or drugs, venesection and methods for removing serous exudate from the lungs. Oxygen, if slightly administered, will generally lessen cyanosis, but the lung surface available for absorption is so small that the oxygen must be given in high concentration. Venesection gives real relief to men with deep cyanosis and a full pulse, but appears to be harmful in col lapsed cases with poor pulses, and it should not be postponed until the patient passes into the dangerous state. Gas casualties, who show neurasthenic or cardio-vascular weakness after several weeks' treatment at the depot should be transferred to home hos&als.
Emma) S. Faintow, Consulting Military and Civil Engineer.