RESPIRATORY METABOLISM OF PLANARIA AGILIS. 2OQ 



for example by the velocity constant in the equation for a bi- 

 molecular chemical reaction, Krogh ('19). In the absence of 

 appropriate experimental data further discussion of this question 

 is unprofitable. 



\Yhatever may be the ultimate explanation or cause of the 

 drop in the curve toward the origin of the axes, such curves for 

 different animals nevertheless may turn out to be useful in 

 interpreting the role of oxygen concentration as a factor in 

 determining the distribution of the organism, and if further 

 experiment can show that difference in concentration of oxygen 

 between the outside and inside of the animal does not act as the 

 limiting factor, but rather the concentration of oxygen as such 

 in the cells, then such curves will be very important criteria for 

 the differentiation of different types of respiratory metabolism 

 among animals. A careful comparative study of, for example, 

 the terrestrial, semi-aquatic, and mud-dwelling species of earth- 

 worms might throw further light on the question. 



THE RATE OF OXYGEN CONSUMPTION BY PLANARIA IN 



AERATED WATER AFTER LIVING IN WATER 



OF Low OXYGEN CONCENTRATION. 



Planaria agilis shows a characteristic increase in the rate of 

 oxygen consumption after removal to aerated water from oxygen- 

 free water. This is illustrated in Table I. The experiment was 

 divided into three consecutive test periods. During the first 

 period tests on the seven lots of animals were made in air-satu- 

 rated water. After eight hours the lots were transferred to a low 

 concentration of oxygen for periods of seven, nine and twelve 

 hours, and at the end of these test periods they were transferred 

 directly into aerated water and the rate of oxygen consumption 

 per gram per hour determined for a third period of four hours. 

 Table I. is a complete statement of the results. 



It will be noted that during the third period there is an increase 

 in rate over that in the first period varying from 49 to 85 per 

 cent. There is no proportionality between this percentage 

 increase and the length of time which the animals were subjected 

 to the low oxygen concentration as one might at first expect. 



