ON THE ACTION OF CERTAIN SUBSTANCES ON OXYGEN CONSUMPTION. VI. THE ACTION OF ACIDS. L. H. HYMAN, DEPARTMENT OF ZOOLOGY, UNIVERSITY OF CHICAGO. In recent years the role of acidity and alkalinity in biological processes has been the subject of numerous investigations. The impetus to this field of research was given by the invention of methods for determining the true hydrogen ion concentration of biological fluids and materials. As a result of the great mass of work accumulating along this line of research, there prevails among biologists the impression or opinion that hydrogen ion concentration is of tremendous importance in the life of or-ganisms. Yet, looking back upon the history of science, one may be pardoned for a certain degree of skepticism. Biologists appear prone to attach undue significance to whatever field of investigation happens to be the fashion of the decade and time alone can assign a mass of research on one particular topic to its proper place. The present series of experiments was undertaken in part as a test of the proposition that hydrogen ion concentration is of fundamental importance in physiological processes. The con-sumption of oxygen in respiration was chosen as a physiological process essential to the organism in the highest degree and readily susceptible to quantitative measurement. An attempt was made to determine: (a) whether increasing the acidity of the environment of an organism has any effect upon the rate of oxygen consumption ; (b) whether this effect is assignable to the free hydrogen ions or to some other factor. The experiments prove that alterations in external acidity markedly affect the rate of respiratory metabolism of animals; but they also show that the free hydrogen ions are little, if at all, responsible for the observed effect. 288
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