OXYGEN CONSUMPTION IN ACIDS. 321 



17. Butyric acid has almost no action on the oxygen con- 

 sumption of Planaria. No explanation has been discovered for 

 this fact. 



1 8. The different acids employed are lethal for Planaria in a 

 given arbitrarily selected time (2 to 3 hours) at different hydrogen 

 ion concentrations. The order of toxicity and the hydrogen ion 

 concentrations at which the acids are equally lethal are: butyric 

 (5.0), acetic (4.4), tartaric (3.6), citric (3.4), sulphuric (3.2) 

 and nitric and hydrochloric (3.0). 



19. The facts given in 18 prove that the hydrogen ion is not 

 the cause of death but either the anion or the molecule of the 

 acid is involved. Penetrability is probably also a factor. Death 

 in acids appears to be due to coagulation. 



20. The order of toxicity of the acids and the pH at which they 

 are equally lethal are the same in ordinary and in carbonate-free 

 water, showing that death is not due to carbon dioxide liberated. 



21. Acidification of natural waters constitutes a method for 

 depressing the rate of oxygen consumption of aquatic animals for 

 experimental purposes. 



22. The experiments herein presented cast doubt on the 

 supposed importance of hydrogen ion concentration per se in 

 biological processes. 



BIBLIOGRAPHY. 

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