88 VITALITY AND EFFICIENCY WITH RESTRICTED DIET. 



shown that the percentage of oxygen in the residual air at the end of a 

 10-minute or even 15-minute experiment is always very considerably 

 above that of the oxygen in outdoor air. Consequently subjects can 

 never suffer from oxygen- want. 



EXPERIMENTAL PROCEDURE. 



The use of the apparatus should be preceded each day by a test for 

 tightness which is easily made by placing a 100-gram weight on top of 

 the spirometer. If there is a leak at any point the spirometer will 

 show it definitely in 3 minutes. After the weight is removed, the 

 motor is started and approximately 2.5 hters of pure oxygen admitted 

 from the cylinder through the pet-cock, P (fig. 3). As each millimeter 

 on the scale corresponds to approximately 21 c.c. (the exact value is 

 determined at the time of construction),^ this amount of oxygen is 

 sufficient to raise the bell approximately 120 mm. The oxygen is best 

 introduced when the spirometer bell is about one-third of the distance 

 above its lowest level, as this allows for exaggerated expiration or 

 inspiration without completely filling or emptying the spirometer. 



Since the apparatus is primarily designed for measuring oxygen only, 

 for the time being we need not consider the method of measuring the 

 carbon dioxide. The connection of the subject with the air circuit is 

 controlled by the 3-way valve (see V, fig. 2), which may be opened 

 directly to the room air or, by turning it 90 degrees, connected with the 

 ventilating air circuit. A small double-headed arrow, stamped on the 

 top of the valve, indicates in which direction it should be turned. The 

 opening to the room air usually points down and is not shown in figure 2. 

 A short elbow is attached to this opening and over the end of the elbow 

 a small piece of goose-down is fastened with a bit of wax. The move- 

 ments of this feather indicate the respiration rate and the end of each 

 expiration. 



With the breathing appliance attached, the subject is first allowed to 

 breathe room air through the side opening of the 3-way valve. The 

 temperature of the spirometer bell and the position of the pointer on 

 the scale are recorded, also the barometer,^ which should be read to the 

 nearest millimeter. As soon as the respiration appears normal, the 

 3-way valve is quickly turned 90 degrees to connect the subject with 

 the air current. This should be done at the end of a normal (not 

 forced) expiration. At the moment of turning the valve, the exact 

 time is noted, preferably with a stop-watch. Practically no further 

 attention need be given to the subject or apparatus until the end of the 

 experiment. It is preferable to have the subject keep awake during the 

 experimental period and we frequently find it necessary to tap on the 

 air-pipe to make sure that he has not fallen asleep. At the end of 10 or 



1 Seven bells made on the same form gave by actual calibration the following values per millime- 



ter: 20.99, 20.97, 20.86, 20.86, 20.8.3, 20.97, and 20.97 c.c, with an average of 20.92 c.c. 



2 A good aneroid barometer reading in millimeters is satisfactory, as an error of 7 or 8 mm. 



introduces an error of but 1 per cent in the final calculations. 



