SPIROMETER UNIT. 39 



tory system of the subject. The readings of the spirometer at the 

 beginning and the end of the experiment are also used in determining 

 the oxygen consumption. This spirometer is shown in figure 10, and 

 in more detail in figure 13. 



The spirometer bell is cylindrical in form and constructed of the 

 lightest-weight sheet-copper, with the seams shellacked instead of 

 soldered, as the heat required for soldering would tend to distort the 

 shape of the bell. The internal diameter is about 166 mm. and the maxi- 

 mum vertical excursion is 135 mm.; the fluctuating volume is therefore 

 2 to 3 liters. The total weight of the bell is not far from 100 gm. 

 It is suspended in an annular bath of water or oil between two copper 

 cylinders, a and 6, the inner cylinder being covered at the top except 

 for the openings of the air-pipes, n and o. The bell is suspended by a 

 silk cord, d, running over a grooved aluminum wheel, e, fastened to an 

 upright, /. The weight is accurately counterpoised by a guide-rod, g, 

 a pointer, h, and a weight, I. When properly adjusted, the bell is in 

 equilibrium at nearly any point. The most perfect equilibrium is 

 arbitrarily adjusted at about the midway position of the bell. The 

 spirometer is connected with the ventilating circuit by means of a tube 

 leading from the three-way valve to a short piece of rubber tubing 

 attached to the elbow, m, at the bottom of the spirometer. The metal 

 tube, n, through which the air enters, is continued to the top of the 

 inner cylinder. The air leaves the spirometer bell through a smaller pipe, 

 o, which can be connected directly to the intake end of the blower. A 

 millimeter scale, p, fastened to the frame of the spirometer and a 

 pointer, h, attached to the guide-rod permit readings of the height of 

 the bell. 



Device for obtaining a graphic record of the respiration. — The spirom- 

 eter bell rises and falls with each respiration; this movement is recorded 

 graphically. To the guide-rod, g, is attached a horizontal piece of 

 steel wire; to the free end of this wire is fastened a small pointer, h, 

 of parchment paper or celluloid. When the bell rises or falls, the move- 

 ment is recorded upon the moving drum of a kymograph, the record 

 showing not only the amount of air inspired or expired, but also the 

 length and depth of the respiration. A specimen record is given in 

 figure 14. On this respiratory curve the beginning of the experimental 

 period is shown at 1. No oxygen was admitted into the apparatus 

 until the point 2, when an attempt was made to add the oxygen as 

 rapidly as the subject consumed it. At 3 the valve was again turned 

 so that the subject breathed into the open air. At 4 a he began breath- 

 ing into the apparatus, but, as will be seen, the valve was turned too 

 soon in the respiratory cycle. No oxygen was admitted into the appa- 

 ratus and at 5, the valve was turned. The subject then breathed into 

 the open air until the valve was again turned at 6 b, the record showing 

 that this was done too late in the respiratory cycle. At 7 the valve 

 was opened to the outside air and the record was ended. The time 

 in minutes is recorded on the lowest line. 



