When the normal lung is studied by means of surface stereomicroscopy1it represents quite a different structural picture than that seen in the ordinary paraffin section of the lung. The ordinary section, which at best is a portion of a millimeter in thickness, shows only a flat view of the lung. The reconstruction study of the lung, in which a careful and painstaking effort is made to fill in the gaps between certain distances, leaves to the imagination the explanation of many facts. The method described in this study supplies not only a surface view, but also a third dimensional view, so that one may see a magnified stereoscopic view extending at least 1 cm. in depth. Thus one is enabled to see a magnified picture of the lung without distortion. THE PLEURAL SURFACE The pleural surface presents a good view of the lung, particularly for the study of the