A stromuhr for measuring blood flow, 1880-1881.
© Science Museum / Science & Society Picture Library
Designed by C Ludwig and made by the Cambridge Scientific Instrument Co. The stromuhr (literally 'flow meter') consists of two glas bulbs joined at the top and connected to an artery at the bottom. The blood flow is calculated from the length of time it takes for the blood from the artery to displace a given quantity of saline solution.