24 COMPARISONS OF RESPIRATORY EXCHANGE. 



Three-way valve. — With this apparatus the subject breathes into the 

 open air up to the beginning of the experiment, but is at the same time 

 attached to the apparatus by either the nosepiece or the mouthpiece. 

 To provide for the instant deflection of the expired air into the closed 

 circuit of the apparatus at the beginning of an experiment, a three-way 

 valve is connected to the piping just before the tension equalizer. 

 This three-way valve is an ordinary three-way plug-cock which is very 

 carefully ground. To diminish the dead space a portion of one opening 

 is cut off and the valve is soldered directly to the tee on the ventilating 

 air-pipe. When it is in position, the side outlet opens directly to the 

 air of the room, and connection is made with the ventilating air-system 

 by turning the valve. In the early development of the apparatus the 

 operator turned this valve by simply placing the fingers on the top of 

 the plug and shifting it when necessary. Later a handle was added 

 so that the valve could be turned without the subject's knowledge. 



Piping, tubing, and couplings. — Standard f-inch piping is used, with 

 an actual internal diameter of 15 mm. The rubber tubing, which is 

 common garden hose, with an internal diameter of 19 mm., is fastened 

 to the piping by wire or by special clamps. The total length of hose 

 used in the apparatus is approximately 2 meters. The fittings are 

 such as are commonly used for brass piping and are all of the same size 

 as the piping. The couplings for connecting the different removable 

 portions of the apparatus are ordinary ^-inch garden-hose couplings. 

 Between the different couplings rubber washers of suitable size are 

 used, care being taken to have them of the best rubber. 



Tension equalizer. — The tension equalizer consists of a rubber dia- 

 phragm fitted to a copper can 16 cm. in diameter and 9 cm. high. In 

 the first form of apparatus ordinary hose-couplings were soldered on 

 to the can at opposite sides near the bottom. Later well-ground 

 unions were attached. A woman's pure-rubber bathing cap, such as 

 can readily be purchased in local stores, is used for the rubber dia- 

 phragm. A cap of medium size permits fluctuation in the volume of 

 respiration and consequently it is necessary to admit oxygen into the 

 apparatus only occasionally. In using the apparatus, care should be 

 taken that the diaphragm does not sink so low as to touch the sides of 

 the metal can and thus produce a suction. The air coming into this 

 tension equalizer contains carbon dioxide, and in order to make sure 

 that it is completely swept out at the end of the experiment, a semi- 

 cylindrical piece of sheet copper is soldered to the bottom and sides 

 of the can near the entrance coupling in such a manner that when the 

 air comes against this sheet it is deflected upward against the rubber 

 diaphragm. This insures a circulatory movement of the air inside 

 the tension equalizer. The tension equalizer with the three-way valve 

 and mouthpiece are shown in figure 5. 



Rotary blower. — The blower first used in the tension-equalizer unit 

 was the so-called positive type, and has previously been described in 



