60 COMPARISONS OF RESPIRATORY EXCHANGE. 



absorption of oxygen which requires about 10 minutes, takes place. 

 The pinchcocks, e and e, are now opened and the gas is drawn into 

 burettes 3 and 3 by the routine carried out after the carbon dioxide 

 had been absorbed. When the gas has all been drawn into burettes 

 3 and 3, the water in the phosphorus pipettes, / and /, is drawn to a 

 definite point in the capillary tube and closure is made by shutting the 

 pinchcocks e and e. A reading is then taken of the gas in the burettes 

 3 and 3 and of the analysis thermo-barometer 4. The gas is finally 

 expelled into the open air by opening the pinchcocks / and /. The 

 water-level in the burettes 3 and 3 is finally set at zero, and the appa- 

 ratus is ready for another analysis. 



GENERAL ROUTINE OF AN EXPERIMENT. 



The general method of carrying out a respiration experiment with 

 the Zuntz-Geppert apparatus is as follows: In rest experiments the 

 subject usually lies on his back upon a couch for about half an hour 

 before the experimental period begins. The valves are placed in a 

 convenient position for the subject and so that he does not support 

 them. The outgoing valve is connected to the moist gas-meter by a 

 piece of rubber tubing 20 to 25 mm. in diameter and of suitable 

 length, usually from 1 to 2 meters. When the period for the experiment 

 is determined, the subject inserts the mouthpiece, puts on the nose- 

 clip, and begins breathing through the valves. Usually outdoor air 

 is supplied. The operator then takes readings of the Elster meter 

 every minute. When these become constant, the actual experimental 

 period is begun. The overflow tube, N, from the burettes in the gas- 

 analysis apparatus is raised to such a height that when the pinchcocks 

 a and a are opened air will be drawn into burettes 1 and 1 . The time 

 is noted and a reading of the Elster meter is taken at exactly the 

 beginning of the period. A reading of the meter thermo-barometer is 

 also taken. Pinchcocks a and a are then opened and the air drawn 

 into the burettes 1 and 1. Readings are made of the Elster meter 

 every minute throughout the experimental period, which is usually 

 of 15 to 20 minutes' duration. The time required for emptying the 

 burettes must be so regulated that it will coincide with the duration 

 of the period. This is done by the proper adjustment of the endless 

 cord, r, r, r, upon the concentric pulleys, U, at the back of the meter. 

 When burettes 1 and 1 are full of air, the pinchcocks are closed, the 

 time is noted, and the readings are taken of the meter and the meter 

 thermo-barometer. The experimental period is then ended. 



Several experiments may be made in succession by drawing air into 

 the sampling burettes as soon as the first two samples have been sent 

 over into the potash pipette. A short interval should be allowed for 

 the gases in the burette to reach constant temperature or constant 

 readings. A new experiment may then be begun. 



