SPIROMETER UNIT. 41 



wheel, r. The middle portion of this wire is kept in contact with the 

 guide-rod, g, g, by means of a spring. The outer or free end of the wire 

 has two platinum points which dip into two mercury cups. When the 

 spirometer moves downward and the rod upward, these two points 

 are lifted out of the mercury cups, thus breaking the circuit in which 

 the two cups are installed. When the rod moves downward, the two 

 platinum points dip deep into the mercury and the circuit is closed. 

 The constant make and break of this circuit can be made to actuate a 

 small magnet. Ultimately a mechanical counter of some type will be 

 installed in the circuit which can be read at the beginning and end of 

 an experiment, the difference between the two readings giving the 

 number of respirations for the whole experiment. 



Mechanical arrangement of the apparatus. — A general view of the 

 spirometer unit is shown in figure 16. Standard ^-inch piping is used 

 throughout the apparatus, except for the tube leading from the three- 

 way valve to the spirometer. Half -inch garden-hose couplings connect 

 the several parts. For assistance in manipulating the apparatus with 

 subjects at varying levels, the portion of piping which runs either side 

 of the three-way valve is arranged so that it forms a part of a flexible 

 arm with a movable joint at the point where it is attached to the 

 table. This is counterpoised by the weight, N, and may be fixed in any 

 position by the clamp, 0. Loosening the couplings either side of the 

 three-way valve permits the raising or lowering of the three-way valve 

 and the nosepieces. The air, on leaving the three-way valve, passes 

 through the tube, L, and the supplementary rubber tube into the 

 spirometer, M. From the spirometer it descends to the pipe below 

 the table and into the rotary blower, A. It then passes through the 

 trap, B, and into the two Williams bottles, C and D. The air from this 

 point passes upward to the three-way valve, S, and then into the carbon- 

 dioxide absorber, E, and subsequently into the Williams bottle, F. 

 The sodium-bicarbonate can for removing the acid fumes is shown as G. 

 The air then returns along the table to the pipe H and back to the 

 three-way valve. The handle of the three-way valve is shown at J. 

 The device containing barium hydroxide is shown at R. 



Care of the apparatus. — In the manipulation and running of the 

 apparatus for routine work a number of points should be observed for 

 keeping the apparatus in good mechanical condition. The blower 

 should occasionally be oiled internally through the oil-cup situated 

 just above the blower. The shaft should also be oiled at times by 

 unscrewing the two rods which close the openings around the shaft. 



The Williams bottles on the lower section of the table in which the 

 water is absorbed from the circulating air-current should be refilled 

 occasionally. The usual routine is to renew the first bottle each day 

 when a series of experiments is being carried on. A record is also kept 



