The method of calculating the amount of oxygen consumed in one period of an actual experiment may be illustrated by period 1 of the experiment with Bro on January 8,1918. (See table 3.) In the two earlier periods of this experiment, the mask was employed; in this period the mouthpiece was used, and two sets of records were made, one being included in the other. The intermediate measurement1 is designated for convenience "period la".

Table 3. - Calculation Of Oxygen Consumption In Experiment With The Portable Respiration Apparatus

Subject: Bro. Date of experiment, Jan. 8, 1918.

Apparatus used: Portable respiration apparatus No. 1. Breathing appliance: Mouthpiece.

No. of period: 1, la. Period 1 began 6 a.m.

Duration period 1....... 15'16" (15.27')

Duration period la...... 8' 8" ( 8.13')

Height of spirometer bell.

Temperature of spirometer.

Period 1.

Period la.

Period 1.

Period la.

Beginning...

984 mm.

942 mm.

Beginning...

75

78

End...........

820 mm.

853 mm.

End..........

82

80

Difference...

164 mm.

89 mm.

Av. (°F.)......

78.5

79

Av. (°C.)......

25.8

26.1

Barometer 740.6 mm.

Logarithms.

Period 1.

Period la.

Difference in height of spirometer bell...................

..........2.21484

1.94939

Volume per mm. height of spirometer bell.............

..........1.32056

1.32056

To reduce to 0o C...

.........9.96071-10

9.96027-10

To convert to 760 mm. pressure................

..........9.96877-10

9.98877-10

Decrease in volume at 0° C. and 760 mm. (oxygen consumed).

..... 3.48488

3.21899

Duration of period..

............1.18384

0.91009

Oxygen consumed per minute..

2.30104

2.30890

=200c.c.

= 204 c.c.

Correction for reduction of total vol. of air to 0° C. and 760 mm.

(+ c.c for each rise of 1 o F)....

+7

+2

207 c.c.

206c.c

Average of two measurements of oxygen consumed per minute..

. 207 c.c.

1In this case but one intermediate period instead of two was recorded.

The apparatus and breathing appliance used, the date, and the num ber of the experimental period are first recorded, also the subject's name. The times of beginning and ending the experiment are likewise recorded, that is, the exact moment the valve is turned connecting or disconnecting the subject with the air-current. The duration of the two measurements of oxygen are given, the figures in parentheses showing these times with the seconds reduced to decimals for convenience in calculating.

In the middle section records are made of the height of the spirometer bell and the temperature of the spirometer (°F.) at the beginning and end of the complete period and the intermediate period. From these records the average temperature (centigrade) of the spirometer and change in height of the spirometer bell are calculated for the two measurements.

In the lower section the cubic centimeters of oxygen per minute are computed by logarithms. The decrease in the volume of air is first calculated from the difference in height of the spirometer bell by means of the factor for this spirometer (20.92 c.c. for each millimeter of change), then reduced to 0° C. and 760 mm. pressure, using the average temperature of the spirometer during the measurements and the barometer record obtained for the period. Thus the logarithm of the spirometer difference for the total period (164 mm.) is 2.21484; the number of cubic centimeters represented by each millimeter of difference for this spirometer is 20.92, with a logarithm of 1.32056. The logarithm for the factor used to reduce the average temperature of the spirometer to 0° C. (9.96071 - 10) and that for the factor to reduce the observed pressure to 760 mm. (9.98877 - 10) are also found from tables prepared for the purpose. The total of the four logarithms gives the logarithm (3.48488) for the decrease in volume of the air in the apparatus during the period, at 0° C. and 760 mm. pressure, this being equivalent to the volume of oxygen consumed. No correction is made in this calculation for the tension of aqueous vapor, as it is assumed that the air as measured is dry.1 From the logarithm of this volume is subtracted the logarithm 1.18384 for the duration of the measurement (15' 16"), the result giving the logarithm for the cubic centimeters of oxygen consumed per minute, in this case 200 c.c.

A further correction in the results obtained by this method of calculating is necessary, inasmuch as the total volume of air in the spirometer and air system should be reduced to 0° C. and 760 mm. pressure at the beginning and end of the period to obtain the true shrinkage in the volume of air. Such computations have been made for 14 experiments in which from 198 to 272 c.c. of oxygen were used and with temperature fluctuations ranging from 3° to 19° F. It was found that the difference as a result of making this reduction corresponds to +1 c.c. of oxygen for each degree Fahrenheit of the rise in temperature during the measurement. It is therefore justifiable, for the sake of simplicity, to make an arbitrary correction by adding 1 c.c. of oxygen for each degree of the rise in temperature of 7° F. This gives a value of 207 c.c. of oxygen per minute consumed during the period of 15 minutes and 16 seconds. The same method is followed in calculating the oxygen consumed during the intermediate measurement, i. e., period la. The agreement of the two measurements is excellent, 207 and 206 c. c. oxygen per minute.

1 For the measurement of the total period, this assumption is correct. During the measurements in the intermediate period (a) made by the Emmes method, there is unquestionably a certain amount of moisture in the air. Theoretically corrections should be made for this moisture. It has been shown, however, by means of a sensitive psychrom-eter placed in the air-circuit, that the percentage of moisture is so small that in practice it may be neglected in the calculation of the oxygen consumption during these short periods.

Practical Use Of The Apparatus

From the foregoing description it will be seen that this apparatus dispenses with gas analysis and weighings. By reading the millimeter scale indicating the height of the spirometer bell, the thermometer in the top of the spirometer, and the barometer, we may obtain all the data required for rapidly computing oxygen consumption and heat production. The apparatus is designed particularly for the determination of the oxygen consumption, with special reference to clinical application. It can not be used for the determination of the respiratory quotient as a substitute for either the respiratory-valve method outlined by Dr. Carpenter (a closely fitting mask, Tissot valves, a carefully calibrated spirometer, good gas-analysis apparatus, and a good gas analyst) or the perfected form of the clinical respiration apparatus developed in the Nutrition Laboratory.1 The portable respiration apparatus has, however, the advantages of portability, simplicity, and rapidity of operation, with a degree of accuracy in the determination of the oxygen consumption to meet the needs of practically all scientific work. It was particularly adapted for use in the low-diet research for simultaneously measuring the basal metabolism of seven young men each morning. Four of the apparatus employed for these observations are shown in figure 4 in position, with accompanying beds, in one of the laboratory rooms at the Young Men's Christian Association College, Springfield, Massachusetts.