From: Die Geschwindigkeith des Athemstromes und das Athemvolum des Menschen, by H. Zwaardemaker and C.D. Ouwehand, Archiv für Anatomie und Physiologie, Volume 28, Published by Physiologische Gesellschaft zu Berlin, 1904, page 243.

An early flow measuring device.  When a subject blew through the central tube (a), positive and negative pressure in the opposed pitot tubes (b) caused thin plastic domes (f) to rise or fall. Their movement was transferred to a long, counter-balanced pen which traced a curve on a smoked drum.