TECHNIQUE FOR METABOLISM DURING REST. 81 



the subject every minute automatically by a clock. The clock was in 

 a closed electric circuit, which caused a buzzer to vibrate for a fraction 

 of a second. If the subject was sufficiently awake to respond to this 

 signal, he pressed a small push button held in his hand; this movement 

 was recorded on the drum. 



At the end of the 10-minute period of collection of expired air, the 

 time was accurately noted and the tube leading to the spirometer dis- 

 connected. Connection was then made with the second spirometer and 

 the expired air collected during a second 10-minute period. Through- 

 out both periods the pulse-rate of the subject was frequently counted 

 by another observer. 



While the second spirometer was being used, the height of the first 

 spirometer, the temperature, and the barometer were recorded. A 

 sample of the air in the spirometer was also collected in small Hal- 

 dane samplers over mercury, properly numbered, and placed in suit- 

 able racks for subsequent analysis. Usually three samples were taken 

 from each spirometer. The total volume of air expired in each of the 

 two 10-minute periods could be computed from the height of the two 

 spirometer bells. These volumes could be corrected to 0° C. and 760 

 mm. by suitable calculations. Using these volumes and the number 

 of respirations per minute as obtained from the kymograph records, 

 the total volume of air expired per minute and the total volume per 

 respiration could be accurately determined. 



The gas analyses were all made with the small Haldane portable 

 apparatus. Two of these were kept in perfect condition for the pur- 

 pose and analyses frequently made on both for control. Furthermore, 

 the gas analyses each day were preceded by an analysis of outdoor air; 

 until satisfactory values were found for both carbon dioxide and oxy- 

 gen in these air samples, the analyses of the gas samples were not made. 

 The gas-analysis technique was carried out by Miss Mary F. Hendry, 

 of the Nutrition Laboratory, whose long training, particularly under 

 the skilful guidance of Miss Ahce Johnson, has made her one of the 

 best gas analysts that the Laboratory has ever had on its staff. 



With two and in the latter part of the research three subjects, each 

 observed for two 10-minute periods, the usual duplicate analyses for 

 each spirometer would require a total of 8 analyses with 2 subjects and 

 12 analyses with 3 subjects. It was early found, if the sample from 

 one spirometer was analyzed and the complete oxygen intake and 

 carbon-dioxide production computed from this one analysis, and a 

 sample from the second spirometer analyzed and the complete oxygen 

 intake and carbon-dioxide output computed from the results of the 

 analysis, that in the large majority of cases, one could rely upon a sin- 

 gle analysis of the air sample from each spirometer and assume that the 

 accuracy of the whole physiological and chemical process was estab- 

 lished by the agreement of the two samples. This procedure was not 

 followed until several days' verification of the method had proved its 



