RESPIRATORY METABOLISM OF PLANARIA AGILIS. 2Q"J 



to act as a limiting factor on the rate of oxygen consumption 

 lies somewhere around one third and one fourth of the concen- 

 tration at air saturation, a little higher than that indicated by 

 the curve in Fig. I. Whether or not the respiratory mechanism 

 of Planaria can actually adjust itself by maintaining to some 

 extent a constant rate of oxygen absorption at oxygen concen- 

 trations below that which is limiting in such an experiment as 

 the one given above, is an interesting question and will be referred 

 to again. 



The question arises as to whether or not Planaria can remove 

 the last traces of dissolved oxygen. In general the impression 

 obtained from many experiments of one type or another was, 

 that the very last traces of oxygen could in general not be re- 

 moved. 3 



The slope of the part of the curve shown by the interrupted 

 line is the part which was left in some doubt in this experiment. 

 Hence several separate tests were made on different lots of 

 animals in order to determine more definitely whether high 

 concentrations of oxygen do increase the rate of oxygen con- 

 sumption. In each of the experiments two identical lots of 

 animals were tested at air saturation and high oxygen concen- 

 tration. The following are the results of three separate tests 

 on different lots of worms. 



Concentration of Oxygen Oxygen Consumed per 



at Beginning. Gram per 24 Hours. 



C.c. O2 in 136 c.c. water. 



p- T f 0.820 4.02 



' \ 1.996 4-38 



TT / 0.797 (Air Sat.) 2.92 



' I 1.768 3-36 



Exp. III. .I 1 ' 320 



I 2.920 3-74 



In general the results from several experiments indicate that 

 there is a slightly higher rate of oxygen consumption at concen- 

 trations above air saturation than at air saturation. The approx- 

 imate amount of this increase is indicated by the slope of the 

 broken part of the curve. The experiment clearly shows that 



3 Winkler's method as ordinarily used is however not sufficiently accurate as a 

 means of giving an absolute answer to this question, for iodine from potassium 

 iodide is slowly set free by an excess of acid. 



