RATE OF OXV(JKX CONSUMPTION 



181 



Counter balancing 

 qht 



Vooc.c. 



Graduated 



cylinder 



Fig. 172. Arrangement of apparatus for recording and measuring the rate of oxy- 

 gen consumption. (See also Fig. 175.) The side tube of the trachea! cannula opens 

 into the interior of the large square pan. The trough (Fig. 173) is filled with water 

 and the breathing pan dips up and down in the water. A layer (3/4 inch deep) of 

 strong sodium or potassium hydrate solution is placed in the bottom of the inner pan 

 to absorb the CO 2 exhaled by the animal. If the clip on the tube leading from the 

 graduated cylinder to the pan be closed while the oxygen tank is opened a little, the 

 water in the cylinder will be forced up into the pressure bottle. When the cylinder is 

 thus filled with oxygen the tank valve is closed. The oxygen remains stationary in the 

 cylinder but can be immediately run into the pan by opening the clip on the com- 

 municating rubber tube, as the water in the pressure bottle will quickly run down and 

 displace the oxygen which is thus forced out into the pan. This causes the writing 

 lever on the drum to make a sharp rapid descent. As the animal uses up the oxygen 

 and the breathing pan slowly descends the writing point on the drum slowly goes up. 

 (See Fig. 175.) 



