The introduction of the radiopaque substances, bismuth subcarbonate and iodized oil, 40 per cent, into the lung for pneumonography has been found to be harmless when limited quantities are used. The substances themselves are readily coughed out, and during their sojourn in the lung have a medicinal value (fig. 6).
The bronchoscopic method of introduction gives a direct examination of the trachea and of the main bronchi of each lobe of the lung. In addition to the diagnostic value, the bronchoscopic method permits of the removal of obstructing secretions and granulations, and when an organic stenosis of the bronchus exists, it allows of the introduction of the substance by sight through the stenosis into the portion of lung distal to the narrowed bronchus. By this method the substance can be accurately placed in any desired portion of the lung and a positive pneumonogram obtained with the minimum quantity of opaque