OXYGEN CONCENTRATION AS A LIMITING FACTOR IN THE RESPIRATORY METABOLISM OF PLANARIA AGILIS

¹ DEPARTMENT OF ANIMAL BIOLOGY, UNIVERSITY OF MINNESOTA

1. Oxygen concentration becomes a limiting factor in the rate of oxygen consumption by Planaria agilis at about one third air saturation of water at 20° C.

2. Life in low oxygen concentrations results in an accelerated respiratory metabolism varying from two to eighty-five per cent. when the animals are returned to air. This increase is not proportional to, nor directly dependent upon, the previous length of time which the animals have lived in what practically amounts to an absence of oxygen. Some slight evidence was obtained which indicated that repeated subjection of Planaria agilis to low oxygen concentration may result in a small decrease of the acceleration of oxygen consumption when returned to aërated water after living in very low oxygen concentration.

3. The percentage acceleration of oxygen consumption referred to under 2 is more marked in starved than in fed animals.

4. The rate of carbon dioxide elimination continues at practically the same rate in hydrogen as in air, until loss of irritability and muscular tone begins. The loss of irritability in Planaria agilis is therefore more closely correlated to change in rate of CO₂ production than to consumption of free oxygen if in fact it is correlated closely to either one.

5. The effect of KNC in inhibiting the oxidations in Planaria is not identical with the effects due to the absence of free oxygen.