The majority of the gases which have been utilized in the recent war owe their efficiency to their irritative and escharotic action on the respiratory tract. This action causes an inflammatory edema, which is followed by a cellular exudate, both in the upper air passages and in the pulmonary parenchyma. While the highest mortality occurs in the acute, or edema, stage, a second peak in the mortality curve is encountered with the pneumonia process. The type of the latter inflammatory reaction is largely determined by the extent of the primary destruction. Many gases produce such deep seated necrosis that if death does not ensue in the acute edema stage or at the height of the pneumonia process, organization of the exudate within the alveoli and, more frequently, of that in the bronchioles, may occur. The contraction of the scar may lead to serious and progressive mechanical difficulties, not only with