Within the last twenty years, the importance of a uniform hydrogen-ion concentration in the body fluids, and the mechanism whereby this constant is maintained, have been given considerable attention, and much useful fundamental information has resulted from investigations along this line. The significance of the reaction of the liquid medium in respiration, in enzyme action, in the swelling of colloids and in other vital phenomena of cells has been given detailed attention in the recent literature. Methods of measuring with extreme accuracy and of expressing the reaction of body fluids have been so well developed that the terms have become common in physiologic parlance.
The regulation of this constant is entirely chemical, and there are several systems available in the blood for accomplishing it. L. J. Henderson of Harvard University was one of the first to set forth clearly the part which the phosphates in the plasma could play in