Found on Flickr.  Image from page 130 of “The principles of health control” (1920).

Fig. 28. — The Spirometer. An instrument for measuring the capacity of the lungs.

“Respiratory tests – to measure breathing capacity. Fill the lungs completely full of air, and then force as much of it as possible into a spirometer (Fig. 28) noting the number of cubic inches registered.  To avoid the danger of germ transmission, the mouth-piece should be dipped each time into some disinfecting solution, such as a four per cent solution of carbolic acid in water, and then wiped dry with a towel. Instead of the solution, individual wooden mouthpieces, obtained at slight expense from supply houses, maybe used.”