persisted for days in any locality where used and had very little odor and was not unpleasant at the time. The masks were very uncomfortable when worn for long periods. Also, the mustard gas affected all parte of the body, easily permeating the clothing. Hence tremendous casualties were caused by its use. Adequate protection never was devised. Difficulties of manufacture fortunately limited the German supply.

7. Toxic smoke {Blue Cross), in July 1917. Some of these toxic smokes produce intense and intolerable (an unprotected man could not fight) irritation of the nose and throat in concentrations only one twenty-thousandth of the lethal concentration of chlorine. All the masks previously mentioned permitted the penetration of smokes. Thfc Germans discovered smokes terribly irritating to the nose and throat and commenced their use on a very large scale. The Germans manufactured

14,000,000 Blue Cross shell and expected extremely important results, hoping to force the removal of the mask and permit casualties to be readily produced by other gases.

The British had forseen this possibility and had provided a partial protection in the shape of an extension to the Small Box Respirator. Subsequently other changes were introduced. Really adequate protection never was devised. Fortunately the German shells were not effective. (Penetration of the mask is effective only when the particles are approximately of a certain size.)

The above facts illustrate grimly the strenuous race that took place between offensive and defensive gas warfare in the late war.

Mask Development

The evolution of the British wartime gas mask, as outlined above, is of special interest since it was the British type which was adopted by the American Army upon entry of the United States into the war.

The earliest German respirators consisted of pads of cloth soaked in a sodium thiosulfate—sodium carbonate solution. These were followed by masks of absorbent cloth made in the shape of a snout which fitted over the mouth and nose.

During the fall of 1915, the Germans turned to a canister-type respirator (see Fig. 112). The facepiece of this mask was made of leather treated with tar oil and tallow to render it gastight and watertight. The facepiece covered the entire face including the eyes. Eyepieces, consisting of an outer layer of glass and an inner layer of chemically treated celluloid which prevented dimming, were inserted. Screwed to u socket in the facepiece was a small cylindrical canister containing absorbent chemicals. The air was inhaled and expired directly through this canister. Originally the canister filling consisted of a layer of kiesel-guhr or granules of earth soaked in potassium carbonate covered with

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