Hemorrhage increased p H of arterial blood and usually increased respiratory volume. Injection of 6% gum acacia in 0.9% NaCl gave opposite results. A series of experiments in which anesthesia was produced by decerebration were better defined than when morphine and urethane were administered. It is suggested that Ph is increased by increase in the respiratory volume and change in rate of blood flow through the lungs. Thus arterial p H changes are secondary to respiratory volume changes.