536 



JOHN R MURLIN 



Fig. 15. Tissot Spirom- 

 eter with capacity of 50 

 liters. A, three-way valve 

 connecting air in bell of 

 spirometer with outside 

 air; B, tube leading to in- 

 side of bell; C, counterpoise 

 tube compensating for 

 change in weight of bell; 

 D, siphon tube connecting 

 C with water in tank; E, 

 flat steel band supporting 

 spirometer; F, wheel over 

 which runs E; H, rubber 

 tube connecting siphon tube 

 with supply tube J; /, 

 branch of supply-water tube 

 leading to tank at L ; M, 

 N, overflow tube from tank; 

 O, pointer; P, cock for 

 emptying tank; Q, Q, level- 

 ing screws; R, lead counter- 

 poise; Z, opening for gas 

 sampling. 



to counterbalance the 

 tubes. 



In this form of apparatus the scale for read- 

 ing the volume of expired air is attached to the 

 back side of the counterpoise tube. 



In carrying out an experiment by the Tissot 

 method the valves are first tested for tightness. 

 Boothby carries out this test by filling the gas 

 mask with water and letting it stand for a time 

 for detection of leaks. A three-way valve at. 

 the side of the spirometer permits breathing 

 from the subject into the room air or into the 

 spirometer according to the position of the 

 handle. The mask is attached securely to the 

 face and the subject breathes for a time into 

 the room air with the bell at its lowest posi- 

 tion. The subject continues to breathe into 

 the apparatus for a definite period of time, the 

 inspired air being drawn through a pipe from 

 outdoors. The valve is again turned at the end 

 of an experiment. The temperature of the air 

 is recorded by the thermometer in the top of the 

 bell and a reading of the barometric pressure 

 is taken. 



With the Boothby apparatus several of the 

 lead weights are slotted so that they may be 

 readily removed. When all the weights are in 

 place the bell is in perfect equilibrium at any 

 point of its course, so that when the valve is open 

 to the room air the bell will not change its posi- 

 tion. When one or more of the lead weights are 

 removed so that the bell is no longer perfectly 

 counterpoised it will gradually drop. For the 

 purpose of sampling this is a useful arrange- 

 ment for the weight of the spirometer serves to 

 drive expired air through the outlet tube, thus 

 washing out room air from the main tube and 

 the sampling connections. While the subject is 

 breathing into the apparatus the extra weight 

 of about 300 grams should be placed on the 

 counterpoise so as to induce a slight negative 

 pressure toward the spirometer. This serves 

 resistance which the air meets in the various 



