From the point of view of diagnosis, abscess of the lung should be an acute infectious process associated with the formation of purulent exudate and more or less destruction of lung tissue. In other words, abscess of the lung should not reach a chronic stage without a diagnosis. Early and repeated examinations by means of the roentgen rays are as justifiable as the repeated use of the thermometer and offer a great deal more benefit to the patient who has a suppurative lesion in the lungs. There is much advantage in early roentgen-ray study, not only for the purpose of diagnosis but for the purpose of localization, because a small area of density caused by an exudate is more easily localized than the larger area that develops later. The advantages of repeated examinations are that one can determine the manner of development, the rate of increase of decrease in size,