The word anesthesia--meaning WITHOUT FEELING--describes accurately the effect of ether in anesthetic dosage. Although no pain is felt in operations under inhalation anesthesia, the _*nerve impulses excited by a surgical operation still reach the brain_. We know that not every portion of the brain is fully anesthetized, since surgical anesthesia does not kill. The question then is: What effect has trauma under surgical anesthesia upon the part of the brain THAT REMAINS AWAKE? If, in surgical anesthesia, the traumatic impulses cause an excitation of the wide-awake cells, are the remainder of the cells of the brain, despite anesthesia, affected in any way? If so, they are prevented by the anesthesia from expressing that influence in conscious perception or in muscular action. Whether the ANESTHETIZED cells are influenced or not must be determined by noting the physiologic functions of the body after anesthesia has worn off, and in animals by an examination of the brain-cells as well. It has long been known that the vasomotor, the cardiac, and the respiratory centers discharge energy in response to traumatic stimuli applied to various sensitive regions of the body during surgical anesthesia. If the trauma be sufficient, exhaustion of the entire brain will be observed after the effect of the anesthesia has worn off; that is to say, despite the complete paralysis of voluntary motion and the loss of consciousness due to ether, the traumatic impulses that are known to reach the AWAKE centers in the medulla also reach and influence every other part of the brain. Whether or not the consequent functional depression and the morphologic alterations seen in the brain-cells may be due to the low blood-pressure which follows excessive trauma is shown by the following experiments: The circulation of animals was first rendered STATIC by over-transfusion, and was controlled by a continuous blood-pressure record on a drum, the factor of anemia being thereby wholly excluded during the application of the trauma and during the removal of a specimen of brain tissue for histologic study. In each instance, morphologic changes in the cells of all parts of the brain were found, but it required much more trauma to produce brain-cell changes in animals whose blood-pressure was kept at the normal level than in the animals whose blood-pressure was allowed to take a downward course. In the cortex and in the cerebellum, the changes in the brain-cells were in every instance more marked than in the medulla.