During the course of any operation, the surgeon is responsible for a long chain of ingoing impulses, which travel along the sensory paths from the site of operation to the spinal cord and brain. Morphine diminishes the awakening effect of these impulses by benumbing the perceptive centers in the brain. The correct plane of anesthesia for a patient who has had morphine, for example, one quarter of a grain of morphine sulphate hypodermatically half an hour before narcosis, must appear very superficial as compared with a case to which morphine has not been administered. Not only is considerably less of the anesthetic required, but the lid, for instance, may be quite tonic without indicating that more of the anesthetic is necessary. These observations apply cardinally to anesthesias with chloroform, or chloroform combinations, such as anaesthol.