From http://dgrespiratory.com/other.  The McKesson Vitalor was a dry wedge bellows spirometer.  A pen attached to the top of the bellows marked on a small sheet of graph paper that was attached to an electric motor-driven platen (the curved silver plate).  The mouthpiece was permanently attached to the front of the spirometer.  A reviewer later noted that it was difficult to clean sputum out of the spirometer.