It is commonly appreciated that when a few hundred cubic centimeters of air is injected into the pleural space of persons with tuberculosis of one lung lobe, the slack given by the air to the elastic pull of the hemilung is frequently taken up more by the diseased than by the normal lobes, with the result that the air resides principally over the diseased lobe and collapses it selectively. The roentgenographic appearances in one of these cases are shown in figure 1. The exposure atAwas made of the chest before induction of pneumothorax and demonstrates the presence of a tuberculous lesion lightly infiltrating the right upper lung field; that atBwas made immediately after the last of a series of injections, which introduced 800 cc. of air and occupied ten days and shows marked collapse of the diseased portion of the lung without detectable deflation of the