TECHNIQUE FOR METABOLISM DURING WORK. 133 



time the assistant had adjusted the mill to a speed of 70 meters per 

 minute. At the end of 3^ minutes of walking one assistant read the 

 psychrometer; at the end of 3f minutes a second assistant read the 

 level of the spirometer bell and a third balanced the Wheatstone bridge 

 of the resistance-thermometer circuit. At the end of exactly 4 minutes 

 of walking^ which marked the beginning of the period proper, the tem- 

 perature was taken and the air blowing through the drying circuit was 

 stopped. Air samples were then drawn into the two Haldane gas- 

 analysis apparatus with the necessary precautions. As soon as this 

 was completed the air was again started in the drying circuit, and the 

 analysis of the air proceeded forthwith. 



As it was impossible for the assistant to read both step and distance 

 counters at the same moment, it was the practice to read the step 

 counter 10 seconds before and the distance counter 10 seconds after the 

 4-minute signal. As this was done at the 4, 14 and 24 minute readings, 

 the elapsed time was the same, namely, 10 minutes in each instance, for 

 the experimental period proper. The barometer was read as soon after 

 the 4-minute signal as possible. During the next 10 minutes the 

 assistants were occupied in watching the psychrometer, temperature, 

 counters, and especially the spirometer bell, which rose with the tem- 

 perature of the chamber as the experiment progressed. The tempera- 

 ture was controlled by means of electric fans blowing over the chamber 

 and by opening the windows of the room. On account of the large 

 radiating surface of the chamber and the thorough stirring of the cham- 

 ber air, any tendency of the air to expand unduly could be quickly 

 checked in this way. 



At the close of 6 and 12 minutes of walking photographic records of 

 the pulse were made. As stated earlier, the photographic record thus 

 secured includes also records of the step and respiration rates. During 

 the interval when the pulse was not being photographically recorded 

 the operator made a visual count of the deflections of the string for 15 

 to 20 seconds each minute. By this means and the aid of a stop-watch 

 records were secured for each minute. At 9| minutes after the period 

 began, which was 13^ minutes after the walking began, a reading was 

 taken of the psychrometer; the spirometer was read at 9f minutes after 

 the beginning of the period; and at 10 minutes gas samples were drawn, 

 and the temperature, barometer, and counters were read in the same 

 way as at the beginning of the period on the fourth minute of walking. 

 This marked the end of the first half of the period, and these data were 

 taken as a control and possible check should anything irregular appear 

 later in the experiment. 



^ These 4 minutes of walking were looked upon as a period during which the carbon-dioxide 

 production would have reached a uniform rate. That 4 minutes is sufficient for the 

 purpose is indicated by the fact that both the pulse and respiration rates are fairly 

 uniform by the fourth minute of walking; furthermore, unpublished results of exper- 

 iments made in the Nutrition Laboratory show that the rate of oxygen consumption 

 when a person walks at 30 per cent grade at a rate of 50 meters per minute becomes 

 uniform by the end of the second minute. 



