18 



METHOD OF STUDYING RESPIEATION 



returning through the rubber syringe, F,^ into A. A constant cir- 

 culation^ is kept up by the motion of K, each downward movement 

 of which compresses the syringe, F, forcing a stream of bubbles® 

 through the indicator solution in B ; K is attached at one end to the 

 hinge, L, and at the other to the connecting rod, G, which moves 

 when H is made to revolve by means of a small motor. The syringe, 



Fig. 1. Apparatus for the measurement of respiration and of photosyn- 

 thesis. The organisms are placed in A; by compressing the syringe, F, the CO2 

 is forced through the indicator solution in B, returning through F into A. The 

 wheel, H, is caused to rotate by means of a motor; the resultant motion of K 

 compresses F and keeps up a constant circulation of gas. 



* This has valves at the outlet and inlet. In place of the syringe a tambour- 

 bellows, pump, miniature fan, or other simple device may be employed. 



* It is desirable to have the gas circulate at a constant rate. The rate may be 

 controlled in a number of ways; it may be tested by observing the rate at which 

 the color of the indicator changes, when a stream of air, free from CO2, runs 

 through it. 



« If the stream of bubbles does not flow satisfactorily some of the solution may 

 be removed so that the top of the tube is brought nearer to the surface. Inclining 

 the tube, B, may assist in freeing the bubble as it issues from the tip of the tube. 

 The compression of the syringe may also be increased and a syringe with stifTer 

 walls may be used. If this does not produce the desired result the elasticity of the 

 system must be increased by making the rubber connections longer, or by using 

 softer rubber; or, better, a small elastic bulb may be introduced at any convenient 

 place. 



