OXYGEN CONSUMPTION IN ACIDS. 



303 



It will be perceived by examining these tables that the rate of 

 oxygen consumption of Planar ia is decreased by acidifying the 

 water with hydrochloric acid and that the percentage of depres- 

 sion is greater the higher the acidity. Yet it must be remarked 

 at this point that the percentage of depression obtained with any 

 given concentration of acid is subject to inexplicable variation 

 even on the same lot of worms and quite commonly when 

 different lots of worms are employed. In most cases this varia- 

 tion did not exceed 10 per cent, but it may reach 20 to 30 per 

 cent., in the higher concentrations. On account of these puzzling 

 variations I was frequently compelled to repeat the experiments 

 many more times than had been anticipated as necessary. The 

 matter of variation is considered at more length later and a 

 possible cause is suggested. 



TABLE Y. 



ACTION OF CARBONIC AND ACETIC ACIDS AT DIFFERENT HYDROGEN ION 



CONCENTRATIONS ON THE OXYGEN CONSUMPTION OF Planaria. 

 All figures represent cc. of oxygen consumed per hour at 20 C. Each vertical 

 column constitutes one experiment, giving successive determinations on the same 

 lot of worms. 



Normal Respiration, pH 8.0. 



Respiration in Acidified Water. 



Per cent. Initial Depression. 



Recovery after Return to Normal Water. 



5. Experiments with Sulphuric and Nitric Acids. The action 

 of these two mineral acids was very similar to that of hydro- 

 chloric acid. The percentage of depression induced was con- 

 sistently slightly greater at the same hydrogen ion concentrations 



