OXYGEN CONSUMPTION IN ACIDS. 313 



2. Action of Mineral Acids Added to Carbonate-free Water on 

 the Rate of Oxygen Consumption. The same amount of acid was 

 added to the water as would be required to produce the desired 

 pH in unaltered water. Alkali was then added until the pH in 

 question had been attained. Rather extensive experiments were 

 performed with hydrochloric acid, less extensive with sulphuric 

 and nitric acids. The results in all three acids were the same 

 and were very striking. Acidification of carbonate-free water 

 with these acids has absolutely no effect on the rate of oxygen 

 consumption of Planaria at all concentrations between pH 7.5 

 and 5.0. At pH 4.0, a slight depressing effect was noted, about 

 15 per cent. This result is graphed in Fig. I. 



It is thus proved that practically the entire depressing effect 

 on the oxygen consumption of Planaria produced by the addition 

 of mineral acids to natural water arises from the carbon dioxide 

 set free in such water by decomposition of its contained carbon- 

 ates by the acid added. The depressing effect is thus a carbon 

 dioxide depression. It is probable that the carbon dioxide 

 penetrates the animal in the gaseous state and acts within the 

 animal as such or by inducing an internal acidity (cf. Jacobs, '20). 



3. Action of Organic Acids in Carbonate-free Water. Only 

 acetic and butyric were tried. I was particularly interested in 

 testing these two acids as they are believed to penetrate organisms 

 readily. The result should serve to indicate whether the effici- 

 ency of carbon dioxide is merely a question of penetrability. 

 Unfortunately decisive results could not be secured, owing to the 

 fact, already mentioned, that very little depressing effect was 

 obtained in the controls. Butyric acid, previously found to be 

 the least effective of all of the acids tried, was in this series of 

 experiments quite ineffective in normal water. Even at pH 5.0, 

 an injurious concentration, no depression of the oxygen con- 

 sumption in n'ormal water appeared. Consequently the action 

 of butyric acid in carbonate-free water could not be determined. 

 With acetic acid, some results were secured. Acetic acid was 

 about half as effective in inducing depression as in the experi- 

 ments of the preceding year. At concentrations weaker than 

 pH 7.0 there were again indications of acceleration of the rate 

 of oxygen consumption in the controls. At acidities of pH 6.5 



