Until very recently, no satisfactory method had been devised for improving the condition of patients suffering after operation from the bad effects of ether anesthesia. The use of carbon dioxid for this purpose was proposed two years ago by Henderson and Haggard.1 The physiologic principles which suggested this method are (1) that ether, being a volatile substance carried by the blood, will be eliminated chiefly through the lungs; (2) that the rate of its elimination must, therefore, vary directly with the volume of pulmonary ventilation. Carbon dioxid being the natural stimulus to the respiratory center, its addition in small quantities to the inspired air seemed to them the logical method of accomplishing this purpose. The present research was undertaken in an effort to discover whether such a use of carbon dioxid in patients suffering from the effects of ether anesthesia could be of outstanding benefit, and whether it was