From a Fenyves & Gut sales brochure kindly provided by Emanuele Isnardi.

“Construction: A transparent plastic box on castors houses two bags containing a maximum of 100 litres each for the inspiratory and expiratory air respectively. A valve system connects the bags to a pneumotachograph which measures the inspiratory and expiratory air. A three-way stopcock makes it possible to let the patient breathe ambient air or air from the bag according to choice. The expirate can be collected in the expiratory bag or released to the atmosphere. Device for filling and fan for deflating the bags. The gas concentration can be measured in the bags and continually monitored at the mouth. Additional equipment: gas analyser, depending on test objectives (see under A), multi-channel compensated direct recorder (see under R), computer for direct MV determination.”