I. INTRODUCTION For the conscientious surgeon, the end of the operation is only the beginning of a period of special attention to the patient. Pulmonary complications form one of the important problems of this time. Excellent analyses of such complications have appeared in recent years from several clinics.1 Of all patients operated on, about 3 per cent. develop some type of pulmonary complication, and one of every 200 operations results fatally from this cause. These facts alone suffice to demonstrate the importance of this subject. There are unquestionably several etiologic factors responsible for these postoperative pulmonary conditions, and those interested in the subject have divided the resultant complications into various clinical groups. Many of these groups have been carefully studied, but in spite of the general interest in postoperative pulmonary complications as a whole, there remains a special group of cases, classified as massive collapse of the lung, which