_Roentgenography_.--All cases of chest disease should have the benefit of a roentgenologic study to exclude bronchial foreign body as an etiological factor. Negative opinions should never be based upon any plates except the best that the wonderful modern development of the art and science of roentgenology can produce. In doubtful cases, the negative opinion should not be conclusive until a roentgenologist of long experience in chest work, and especially in foreign body cases, has been called in consultation. Even then there will be an occasional case calling for diagnostic bronchoscopy. Antero-posterior and lateral roentgenograms should always be made. In an antero-posterior film a flat foreign body lying in the lateral body plane might be invisible in the shadow of the spine, heart, and great vessels; but would be revealed in the lateral view because of the greater edgewise density of the intruder and the absence of other confusing shadows. Fluoroscopic examination will often discover the best angle from which to make a plate; but foreign bodies casting a very faint shadow on a plate may be totally invisible on the fluoroscopic screen. The value of a roentgenogram after the removal of a foreign body cannot be too strongly emphasized. It is evidence of removal and will exclude the presence of a second intruder which might have been overlooked in the first study. Fluoroscopic study of the swallowing function with barium mixture, or a barium-filled capsule, will give the location of a nonroentgenopaque object (such as bone, meat, etc.) in the esophagus. If a flat or disc-shaped object located in the cervical region is seen to be lying in the lateral body plane, it will be found to be in the esophagus, for it assumed that position by passing down flatwise behind the larynx. If, however, the object is seen to be in the sagittal plane it must lie in the trachea. This position was necessary for it to pass through the glottic chink, and can be maintained because of the yielding of the posterior membranous wall of the trachea. THE ROENTGENOGRAPHIC SIGNS OF EXPIRATORY-VALVE-LIKE BRONCHIAL OBSTRUCTION The roentgenray signs in expiratory valve-like obstruction of a bronchus are those of _an acute obstructive emphysema_ (Fig. 74), namely, 1. Greater transparency on the obstructed side (Iglauer). 2. Displacement of the heart to the free side (Iglauer). 3. Depression and flattening of the dome of the diaphragm on the invaded side (Iglauer). 4. Limitation of the diaphragmatic excursion on the obstructed side (Manges). It is very important to note that, as discovered by Manges, the differential emphysema occurs at the end of expiration and the plate must be exposed at that time, before inspiration starts. He also noted that at fluoroscopy the heart moved laterally toward the uninvaded side during expiration.*