METHODS AND APPARATUS 
29 
shown by the graphic records obtained. In experiments with severe mus- 
cular work, however, when the respiration-rate and the ventilation of the 
lungs are greatly increased, it was found much more satisfactory to resort 
to the original form of tension-equalizer. 3 This tension-equalizer is shown 
detail in fig. 3. At each side of the valve m attached to the main 
m 
Fig. 3. — Tension-equalizer and flexible mouthpiece. 
The air from p passes through the 3-way valve r and continues along the pipe b by the opening of the 3-way 
valve m until it enters through e the tension-equalizer can c with the rubber diaphragm h over it. It 
leaves the tension-equalizer through the opening /, passing through the pipe b and on to the blower. The 
mouthpiece g is attached to a tee n, which is in turn attached by short lengths of rubber tubing (k and *) 
to the two 3-way valves r and m. After the experiment has begun and the subject is breathing through 
the mouthpiece and the pipe k, the 3-way valve r is suddenly turned so as to deflect the air through s, n, 
and k, thus diminishing the dead space. The flexibility of s and k permit considerable lateral motion of 
the head. 
ventilating pipe is a brass union a, which is easily uncoupled. To one of 
these is soldered a thin-walled brass tube b, which is passed through two 
holes in the opposite sides of a copper can c, and soldered into place. At a 
point in the pipe midway across the can is placed a plug of wood, cork, or 
rubber, d, openings into the can being provided by two holes e and/. A 
rubber bathing-cap h is fitted over the top of the can and secured by several 
rubber bands so as to obtain perfect closure. The air, entering the tension- 
equalizer from the ventilating pipe at e, circulates freely about the confined 
space in the can and the rubber diaphragm, and passes out the other side at 
/, direct passage through the pipe being prevented by the plug d. This can 
with the rubber diaphragm contains approximately 6.5 liters, so that a large 
volume of air can be taken from the system without producing any tension. 
Furthermore, the weight of the rubber diaphragm is so slight as to pro- 
duce no material amount of pressure or resistance to the respiration, the dia- 
phragm falling with each inspiration and rising with each expiration. The 
inequalities in the shape preclude the possibility of estimating accurately the 
height of the diaphragm at any given time, so that it is necessary to resort 
to a measurement of the inside tension. This is accomplished by connecting 
a Benedict, Am. Journ. Physiol., 1909, 84, p. 357. 
