From: Catalogue of Sharp & Smith, Importers, Manufacturers, Wholesale and Retail Dealers in Surgical Instruments, Printed by Blakely Printing Company, 1889, Page 529.

Advertisement from: The Homoeopathic Guide, Published by Munson & Co., 1881.  Fronticepiece.

To use Marsh’s spirometer the subject exhaled into the balloon.  A measuring tape attached to the balloon measured the circumferance and therefore the volume exhaled. A criticism from elsewhere was that the balloons broke frequently and that it required 20 mm Hg of pressure “before any test of the expired breath can be recorded”.