REGULATION OF THE HYDROGEN ION CONCENTRATION AND ITS RELATION TO METABOLISM AND RESPIRATION IN THE STARFISH.

The normal reaction of the coelomic fluid in Patiria miniata and Asterias ochraceus is pH 7.6, and of the caeca, 6.7, compared with sea water at 8.3, all without salt error correction. A medium at pH 6.7-7.0 is optimum for the caeca for ciliary survival and digestion of protein, and is maintained by carbon dioxide production. The optimum pH found for carbon dioxide production is a true one for the effect of hydrogen ion concentration on the tissue. It does not represent an elimination gradient for carbon dioxide. Because the normal excised caeca maintain a definite hydrogen ion concentration and change their internal environment toward that as an optimum during life, there exists a regulatory process which is an important vital function.