NORMAL PROCESSES OF ENERGY METABOLISM 535 



inspired air could also be readily measured at the same temperature and 

 pressure preliminary to analysis. The bell of each spirometer was counter- 

 poised and provision was made by mechanical means for compensating 

 the increase or decrease in weight of the bell according as it was lifted 

 from or depressed into the water jacket. The Tissot method as used in the 

 French laboratories has been fully described by Carpenter (a). The spi- 

 rometers are of special design and used principally in two sizes, one of 50 

 liters and another of 200 liter capacity. The height of the bell in the 

 former is 60 cm. and the diameter 33 ; while in the 200 liter instrument 

 the bell is 73 cm. high and 65 in diameter (Fig. 15). Air is admitted 

 to the bell through a tube which terminates at the bottom of the spirom- 

 eter in a 3-way stop-cock, A. The major portion of the weight of the 

 spirometer bell is counterpoised by the weight R. The automatic adjust- 

 ment of the counterpoise for the spirometer bell is accomplished by means 

 of a water siphon. A glass cylinder, C, is made of such size that when 



Fig. 14. Metal air valve of Thiry. 



filled to the level of the spirometer the weight of the water in the cylinder 

 exactly equals the increase in the weight of the spirometer bell due to its 

 new position. When the bell rises or falls water is added to or taken from 

 the cylinder C, by means of the siphon tube, D. Any increase or decrease 

 in the weight of the bell due to the varying displacements of the volume 

 of water by the mass of metal in the spirometer bell is thus exactly counter- 

 poised by a like increase or decrease in the weight of water in the cylinder. 

 The upright position of the counterpoised cylinder, C, is determined and 

 maintained by means of two brass rods on which the cylinder travels. This 

 siphon tube, D, is so arranged that it does not touch the cylinder, C, at any 

 point. 



A clinical form of spirometer or gasometer used by Boothby differs 

 from the original form of Tissot in only minor features. A spirometer 

 mounted on wheels as used in the Mayo clinic is illustrated in Fig. 16. 

 The counterpoise of the bell in this instrument is hung over ball bearing 

 wheels by means of steel piano wire. The main weight of the bell is bal- 

 anced by a long hollow brass tube at the upper end of which are placed 

 the necessary lead weights to counterbalance the bell exactly. The siphon 

 arrangement of the original Tissot spirometer is used, but instead of draw- 

 ing water from the gasometer itself to the counlerposed cylinder, water is 

 drawn from a special receptacle. 



