RESPIRATORY METABOLISM OF PLANARIA AGILIS. 2O5 



The animals which were used in the experiments reported in 

 this paper were kept at 20 C. during the experiments, and for 

 from two days to two weeks previous to each experiment in order 

 to avoid any acclimation effects due to temperature. The curve 

 shows that the rate of oxygen consumption was constant up to 

 about thirty-eight hours, at which time the oxygen concentration 

 was equal to about one fourth to one sixth of the oxygen concen- 

 tration of air-saturated water at 20 C. When lower oxygen 

 concentrations were approached the rate decreased. An unused 

 residue of oxygen remained at the end of the experiment. This 

 would have been quickly consumed if the original rate of oxidation 

 had been maintained. 



In this method of experiment the possibility that acclimation 

 of the rate of oxygen consumption to lower oxygen concentrations 

 occurs is not excluded. Therefore the following procedure was 

 adopted. If the animals are subjected suddenly to definitely 

 known low oxygen concentration and the time period during 

 which they are left in this low oxygen concentration is made brief, 

 then acclimation will probably be avoided. The procedure was 

 as follows. Twenty-eight lots of worms with twenty worms in 

 each lot were selected. All the animals were very closely alike 

 in size, history, etc. The experiment was continued for three 

 successive periods of three hours each. During the first period 

 each one of the lots of animals was placed in a bottle containing 

 air-saturated water. The rate of oxygen consumption per gram 

 worm per hour for this period was determined. At the end of 

 the first period the twenty-eight lots of animals were transferred 

 directly into a second set of twenty-eight bottles containing 

 different but known amounts of oxygen per 136 c.c. water. The 

 animals were now left in these bottles for a second period of three 

 hours. There were fourteen different known concentrations of 

 oxygen. Two bottles were used for each concentration in order 

 to increase the accuracy of the determinations. The fourteen 

 different concentrations of oxygen were as follows: 0.029 c.c., 

 0.048 c.c., 0.085 c.c., 0.106 c.c., 0.127 c.c., 0.149 c.c., 0.168 c.c., 

 0.177 c - c -. O- 2I 5 c.c., 0.265 c.c., 0.280 c.c., 0.711 c.c., 1.420 c.c. 

 and 1.840 c.c. per 136 c.c. of water. 



