From The Herald of Health, 1875, January issue, page 93.

A description from: The Science and practice of medicine, Volume 2, 1866, By William Aitken, page 563: “The Lung Tester of A.P. Barnes (to be had of Messrs. Codman & Shurtleff, Boston) is the simplest and cheapest of all spirometric instruments.  It consists of a cylindrical bag of India-rubber cloth, closed at each extremity by a disk of wood, and furnished with two metallic tubes; one tube enters laterally at the bottom, and is about three inches long; the other, vertical, is about twelve inches long, and graduated, and inserted in the centre of the upper disk.  A flexible tube of proper length, with a mouthpiece is stretched over the outer aperture of the lower metal tube, and through this a forced expiration is made; the expired air fills, more or less, the bag and the vital capacity is recorded on the upper tube, which is forced up as the bag expands.  The bag is enclosed in a tin cylinder, shut at both ends with two holes for the tubes.”