50 Gas Analysis. VI 
salve box with a disk of sheet rubber inside, held in place by a 
ring of spring wire soldered to the box at one point. The crack 
round the box is made tight with adhesive plaster. In the 
figure the cover of one valve is removed to show the rubber and 
wire. 
A double valve (inspiratory and expiratory) which also has been 
used in this laboratory is shown in Fig. 3. It is made of two 
pieces of brass tubing (13 and 1 inch interior diameter respec- | 
tively) arranged concentrically. The moving part of each valve 
is a strip of heavy sheet rubber inside the tube covering holes 
Higs 2: 
bored through the tubing and held in place by a metal clip near 
the middle of the strip. The lower ends of the tubes are closed 
with paraffined corks. 
Perhaps no better idea can be given of the extensive use which 
can be made of the open circuit method combined with gas 
analysis than by reproducing here the directions given to the stu- 
dents in the routine course of physiology in this laboratory. These 
directions are typewritten together with the tables mentioned and 
are pasted upon pieces of compo board so that they can be con- 
veniently carried about to the points where work is being done. 
