OXYGEN CONSUMPTION IX ACIDS. 305 



acids. In fact, in these concentrations, there is a tendency 

 towards stimulation of the respiratory rate. Out of nine experi- 

 ments, stimulations of 2 to 12 per cent, were obtained in five 

 cases. The amount of stimulation, however, lies within the 

 experimental variation. The truth probably is that carbon 

 dioxide acidity does not affect the rate of oxygen consumption 

 until the acidity reaches a greater degree than pH 7.0. At 

 greater acidities than pH 7.0, the rate of oxygen consumption is 

 depressed and to a degree similar to that produced by other 

 mineral acids. It was not possible to obtain an acidity with 

 carbon dioxide greater than pH 5.2 with the well water, owing 

 probably to the buffers present in the water. 



7. Experiments with Acetic and Butyric Acids. These two 

 acids were selected as examples of the paraffin acids, supposed to 

 penetrate organisms readily. It was anticipated that the de- 

 pressing effect of these acids would be greater than that of 

 mineral acids. Such, however, was not the case, but the contrary 

 result appeared. Acetic acid, in acidities between 7.8 and 7.0 

 tended to stimulate the rate of oxygen consumption^- Of six 

 experiments performed at pH 7.5, the rate of oxygen consumption 

 was unaffected in two cases, stimulated in two, and depressed 

 in the remaining two. Of six experiments at pH 7.0, all but one 

 were stimulating. It seems probable that low concentrations of 

 acetic acid accelerate, the rate of oxygen consumption. At 

 concentrations greater than pH 7.0, all concentrations depressed 

 the rate of oxygen consumption during the first hour's exposure. 

 During later exposures, a tendency toward acceleration was 

 again manifest. These facts are brought out in Table V. and 

 VI. Butyric acid was the least effective in inducing depression 

 of all of the acids used. This result was very surprising and still 

 remains inexplicable. Butyric acid has only a slight depressing 

 action at all concentrations between pH 7.5 and 5.5. At pH 5.0 

 a depression of 30 to 40 per cent, appears but this concentration 

 of butyric acid is lethal and the worms begin to die within an 

 hour. Acetic acid at pH 5.0 is also injurious. The data on 

 butyric acid are summarized in Table VI., which gives the initial 

 depression induced. Later exposures did not alter the result. 



8. Experiments with Tartaric and Citric Acids. The former was 



