OXYGEN CONSUMPTION IN ACIDS. 309 



the water to 7.8 by addition of such acids induces a measurable 

 lowering of the rate of oxygen consumption. In the case of 

 some acids, notably acetic, less so with carbonic, there was some 

 tendency to an acceleration or stimulation of the oxygen con- 

 sumption at acidities between 7.8 and 7.0. Yet this effect was 

 so slight, and the variability of the results so great that little 

 emphasis can be placed upon this rinding, unless a very large 

 number of experiments were carried out. All of the acids used 

 caused depression at all acidities greater than pH 7.0, but the 

 action of butyric was very slight, almost nil. 



(6) The percentage of depression increases with increasing 

 acidity within certain limits. 



(c) The lower concentrations are, however, relatively more 

 effective than the higher concentrations. This is generally the 

 case wherever chemicals are applied to living organisms. The 

 general form of the curve obtained is seen in Fig. I. This type 

 of curve is so commonly obtained in physiological experimentation 

 that it must possess some deep significance. I am unable 

 however to suggest any explanation of this type of curve. 



(d) The inorganic acids, except carbonic, are in general more 

 effective than the organic, particularly in the lower concentra- 

 tions, pH 7.5 to 6.5. This finding was the contrary of my 

 expectations and contrary to the results of Gray ('24). It is 

 generally believed that organic acids, such as acetic and butyric, 

 penetrate protoplasm readily, while mineral acids are unable to 

 do so. Obviously one would then expect the organic acids to 

 act more powerfully on respiratory metabolism than the in- 

 organic acids. As this was not found to be the case, it must be 

 concluded that the penetrability of the acid has no bearing on 

 the result. The lack of action of butyric acid remains inex- 

 plicable. 



(e) The hydrogen ion concentration cannot be the chief cause 

 of the depression induced, because different acids do not produce 

 the same percentage of depression at the same pH. The result 

 does not substantiate the contentions of Loeb ('22) that the 

 action of acids on colloids depends only on valence and hydrogen 

 ion concentration. According to Loeb's ideas, all of the mono- 

 valent acids, such as hydrochloric, nitric, acetic, and butyric 



