Then, too, there may be chemical noci-associations with enemies now extinct, which, like the ticklish points, may still be active on adequate stimulation. This brief reference to the possible relation of the phenomena of the acute infections to the laws of natural selection and of specific chemical noci-association has been made as a suggestion. Since the doctrine of evolution explains all or nothing, I have included many phenomena to see how reasonable or unreasonable such an explanation might be. Recapitulation The following are the principal points presented: In operations under inhalation anesthesia the nerve impulses from the trauma reach every part of the brain--the cerebrum that is apparently anesthetized as well as the medulla that is known to remain awake-- the proof being the PHYSIOLOGIC exhaustion of and the PATHOLOGIC change in the nerve-cells. Under ether anesthesia the damage to the nerve-cells is at least four times greater than under nitrous oxid. Inhalation anesthesia is, therefore, but a veneer-- a mask that "covers the deep suffering of the patient." The cause of the exhaustion of the brain is the discharge of nervous energy in a futile effort to energize the paralyzed muscles in an attempt to escape from the injury just as if no anesthetic had been given. The exhaustion is, therefore, of the same nature as that from overexertion, but if the nerve-paths connecting the field of operation and the brain be blocked, then there is no discharge of nervous energy from the trauma, and consequently there is no exhaustion, however severe or prolonged the operation may be.