OXYGEN CONSUMPTION IN ACIDS. 3! I 



(ti) The depressing action of acids is completely and promptly 

 reversible, wherever an actual injury to the tissues of the animal 

 has been avoided. Recovery occurs almost immediately, com- 

 monly within the first hour after return to normal water. Several 

 experiments were devised to test the possibility that the de- 

 creased oxygen consumption while in the acid might be compen- 

 sated for by an increase over the normal during the period 

 immediately upon return to normal water. In these experiments 

 the oxygen consumption was first tested in normal water, then 

 in acidified water, of a concentration to give at least 30 per cent, 

 depression, then immediately in normal water again. In most 

 of these cases the respiration had risen to the normal value 

 during the first hour after return to normal water. In a few 

 cases, the oxygen consumption w r as below normal. In no case 

 was any rise over the normal figure observed. 



(i) The experiments justify the use of acids as agents for 

 experimentally producing a state of depression. They also 

 substantiate the generally held view that the effects produced by 

 acids on such processes as cleavage, development, and regenera- 

 tion are assignable to a reduction in the rate of respiratory 

 metabolism. 



EXPERIMENTS WITH Planaria IN CARBONATE-FREE 



FRESH WATER. 



The experiments had reached the point outlined above by the 

 summer of 1924 and I intended to bring the investigation to a 

 close. A number of matters puzzled me greatly but I was 

 unable to devise any means of throwing further light on them. 

 At about this time, however, my attention was drawn to the 

 experiments of Clowes and his associates ('23, '24) in which it 

 was shown that the carbon dioxide set free by acidification of 

 sea-water markedly influences the result and is in some cases the 

 real agent involved. At first I was not inclined to believe that 

 carbon dioxide was responsible for the results which I had 

 obtained with acids. It seemed to me that if carbon dioxide 

 were chiefly or wholly responsible for the observed effects, carbon 

 dioxide acidity should be more effective than acidities produced 

 by other acids and the action of various acids should be similar 



