METHODS OF MEASUREMENT. 39 



system and replaced by fresh oxygen, the absorbing bottles were 

 weighed, and the system was tested for tightness. Approximately 2 

 minutes before the beginning of the walking period proper, the mouth- 

 piece and nose-clip were adjusted. A signal was sent to the operator 

 in the room where the pulse-rate was measured, and in quick succession 

 readings were made of the ventilation adder, the oxygen meter and its 

 temperature, the barometer, and the respiration counter, these readings 

 being verified by a second observer. The kymograph on which the 

 respiration was recorded was also started and the pens were adjusted. 



The walking period proper began when the subject was connected 

 with the ventilating current of air by the opening of the valve at the 

 end of a normal expiration and coincident with the starting of a stop- 

 watch and the reading of the "continuous counter." Within the 

 next 30 seconds, the by-pass B (fig. 1, p. 19) was turned, the kymo- 

 graph was started, which gave a record of the height of the steps, and 

 the step-counter and height-counter were read at 1 minute and 1 min- 

 ute and 10 seconds, respectively. During the period that followed, the 

 operators were occupied in admitting oxygen, recording the body- 

 temperature and pulse-rate, resetting the valve-operating device in 

 readiness for the end of the experiment, adjusting or replacing the 

 kymograph-drum of the step-lift record every 3 minutes, and weighing 

 and testing the carbon-dioxide absorbers for the next period. At 

 about 9 minutes after the period began, the efficiency of the carbon- 

 dioxide absorbers was tested by deflecting a portion of the air-current 

 through a solution of barium hydroxide. At the eleventh minute 

 of the period the step-counter was read; at 11 minutes and 10 seconds, 

 the step-lift counter was likewise read and a warning signal sent to the 

 operator in the pulse-record room. At approximately the twelfth 

 minute, the valve was turned at the end of a normal expiration, a 

 simultaneous reading of the "continuous counter" was made, and the 

 period ended. Readings of the various counters were recorded, and 

 when the carbon dioxide in the system had been completely absorbed, 

 oxygen was admitted to bring the spirometer-bell to its original level. 

 Finally, records were made of the oxygen-meter and its temperature 

 and of the barometer. 



Other periods followed with similar routine; between the periods the 

 subject either sat, stood, or continued walking. During the interval 

 between the periods, if the subject sat or stood, it was usually consid- 

 ered advisable to throw a blanket over his shoulders and around the 

 body, as previously described, for ordinarily he was warm and per- 

 spiring freely after the muscular exercise of walking. Measurements 

 were, as a rule, made in four to six periods during the forenoon. At the 

 end of the morning the subject was released from the treadmill and 

 weighed a second time. A typical record-sheet for one period of a 

 walking experiment, with the necessary corrections and calculations, 

 is given in table 2. 



