340 LOUISE A. ANDERSON. 



Not only is the oxygen consumption of Planana increased with 

 exposure to alkaline solutions but also the susceptibility to toxic 

 agents and conditions is greater when such agents and conditions 

 are applied in alkaline water. In the case of chemical agents, this 

 increased susceptibility in alkaline solution might be ascribed to 

 increased permeability. This explanation does not seem applica- 

 ble, however, to the result with lack of oxygen and ultraviolet 

 radiation. Exposure to these conditions is more rapidly lethal in 

 water of increased alkalinity than in normal water. It seems 

 necessary to conclude that the increased susceptibility of worms 

 to chemicals and to toxic conditions when exposed in water of 

 increased alkalinity is in some way associated with the accelerated 

 metabolism of the animals in alkaline water. Susceptibility is 

 thus again indicated as a method of measuring roughly differences 

 in general metabolic rate. 



SUMMARY. 



1. The general result of exposing Planana dorotoccphala to 

 water whose alkalinity is increased from pH 7.6 or 7.8 to 8.0 to 

 9.2 by addition of NaOH or to 8.0 to 8.8 by addition of NH 4 OH 

 is an increase in the rate of oxygen consumption, whether the 

 exposure is for long or short periods. 



2. The increase lasts as long as the planarians remain in the al- 

 kaline water (longest experiment, two weeks). A return to the 

 normal or to a lower rate (probably result of starvation) occurs 

 at once when the animals are returned to water of the original pH. 



3. The resistance of planarians to lethal concentrations of alkali 

 is not altered by long exposure (ten days) to non-injurious con- 

 centrations of alkali. 



4. The susceptibility of planarians to toxic chemical solutions, 

 to lack of oxygen, and to ultraviolet radiation is greater when they 

 are exposed to these conditions at pH 9.0 than when exposed at 

 ordinary alkalinity of normal water (pH 7.8 to 8.0). 



I desire to express my thanks to Professor C. M. Child and Dr. 

 L. H. Hyman under whose direction the work was done. 



