OXYGEN CONSUMPTION IN ACIDS. 297 



averaged. The percentage of depression is figured from the 

 oxygen consumption during the first exposure to the acid. 



These experiments, although somewhat preliminary in nature, 

 nevertheless exemplify the action of acids on respiratory metab- 

 olism. The conclusions which they furnish were verified by 

 later more extensive w T ork. These conclusions may be briefly 

 stated at this point: 



1. Acidification of the medium lowers the rate of oxygen 

 consumption of animals. 



2. This depression is greater the greater the degree of acidifica- 

 tion up to a certain point. 



3. Low concentrations are, however, relatively more effective 

 than high concentrations. 



4. After a certain degree of acidification has been attained, 

 further acidification does not greatly increase the amount of 

 depression of the oxygen consumption. The maximum depres- 

 sion obtainable is about 50 per cent. 



5. The depressing effect of acids on respiratory metabolism 

 is completely reversible, providing the concentration of acid 

 employed is not actually injurious to the tissues of the animal. 



EXPERIMENTS WITH Planaria IN -UNALTERED FRESH WATER. 



The experiments to be reported in the remainder of the paper 

 were performed at Chicago and occupied the greater part of my 

 time from October, 1923, to February, 1925. The aim of the 

 experiments was to test the effect upon the oxygen consumption 

 of a fresh water animal of the acidification of fresh water with 

 various acids at a variety of hydrogen ion concentrations. The 

 animal selected for this purpose was the flatworm, Planaria 

 dorotocephala. It was chosen for a variety of reasons: it is very 

 abundant, is easily kept under laboratory conditions, has no 

 calcareous parts which might be affected by acid, can be kept 

 quiet during respiratory work, and finally had already served as 

 material for a large amount of physiological experiment. I had 

 originally intended to work also with fish and crayfish but the 

 experiments on Planaria required a much greater expenditure 

 of time than I had anticipated and I did not feel justified in 

 spending any more time on the matter. I was further informed 



