ZUNTZ-GEPPERT APPARATUS. 55 



at one end, d, and closed. In the side of the tube, and about one-third 

 of the length from the closed end, is an elliptical opening, c, which has 

 a smooth edge. A thin membrane is tied around this tube in such a 

 way that it fits loosely; a slit is made in the membrane on the side oppo- 

 site to the opening, c. Zuntz and his co-workers have most commonly 

 used calves' intestine for this purpose, but Durig 1 has substituted fish 

 membrane. We have also employed a very thin tambour rubber. 

 The glass tube is inserted in a rubber stopper, e, which fits into the end 

 of a cylinder, /, 45 mm. in diameter and 19 cm. in length. The other 

 end of the cylinder is constricted to about the same size as the 

 smaller tube. When air is pushed in at e or drawn through the opposite 

 end it distends the membrane, which opens and allows the air to pass 

 through at c. When the pressure in / is slight, the membrane closes 

 and fits against the smaller tube, d. In tying on the membrane there 

 should be a play of several millimeters between the tube and the 

 membrane. One of these valves is attached by rubber tubing to each 

 end of the glass tee, connecting with the rubber mouthpiece. The 

 whole arrangement, with the exception of the membrane covering, 

 is shown in figure 18, the air entering at A and leaving at B. 



Another and more recent form of valve is shown in figure 19. Instead 

 of the outside cylinder being of uniform diameter, an enlargement has 

 been made so that the membrane, when distended, will not adhere to 

 the outer tube. Water can also be placed in the enlarged portion, which 

 assists in moistening the ingoing air and, of still more importance, 

 moistens the membrane in the ingoing air-tube. 



Elster meter. — The gas-meter used for measuring the expired air is 

 shown in figure 20. 2 It has four dials, three of which give 10, 100, and 

 1,000 liters, while the fourth, which is the largest one, gives liters and 

 parts of a liter to 0.02 liter. The meter is filled with water to a certain 

 level, which is determined by opening the cap at A. When water 

 flows out through this opening, the meter is sufficiently full for measur- 

 ing purposes. As different levels require different correction factors 

 and a difference in level is produced by the evaporation of the water, 

 we have attached a side tube with a millimeter scale, W, in such a way 

 as to show the actual level of the water at any time. This water-gage 

 has proved of distinct advantage in working with the Elster meter. 

 The need of some indication of the level of the water in the meter is 

 very clearly shown in the calibration tests made by Cathcart with 

 different levels in the Bohr meter. (See table 7, page 49.) For obtain- 

 ing the temperature of the meter or of the air passing through it, ther- 

 mometers may be inserted as shown in figure 20 at V and V. 



Meter thermo-barometer. — In order to obtain the amount of gas 

 passing through the meter at 0° C. and 760 mm. mercury pressure, 



^urig, Biochem. Zeitschr., 1907, 4, p. 68. 



2 This meter is constructed by S. S. Elster, of Berlin. 



