The form of apparatus used is the same as that employed by dentists and contains both nitrous oxid and oxygen cylinders. A small nasal inhaler is best, although the ordinary mouthpiece will do very well. The gasbag attached to the tank should be kept under low pressure and, as a pain begins, the patient is told to breathe quietly, keeping the mouth closed. As a rule this sort of light inhalation serves to produce the desired analgesic effect. It is not necessary to put the patient deeply under in order to relieve the pain. It is our custom to begin "sunrise slumber" as soon as the uterine contractions become painful. The earlier the gas is started, the more oxygen should be used. Two or three inhalations will suffice to take the "edge" off the earlier and lighter pains. When the pains grow heavier we use less oxygen and permit three or four deep inhalations just before a bearing-down pain. At the first suggestion of a contraction, the patient must begin to inhale the gas; while after the patient has pulled hard on the traction strops--just as the contraction pain is passing--she is given an inhalation containing a larger percentage of oxygen. At the beginning of a pain, pure nitrous oxid is administered, and the patient is instructed to breathe deeply and rapidly through the nose. The gasbags should be about half filled. The mixture of gas and oxygen must be determined by the severity of the pains and individual behavior of the patient. Four to six inhalations of the gas are sufficient to produce the required analgesia in the average case. Following the first few deep inspirations through the nose, the patient can be instructed to breathe through the mouth, while the gas is well diluted with oxygen and continued until the end of the pain. In this way a satisfactory analgesia is maintained throughout the "pain" with a minimum of "gas." The proportion of oxygen used will run from nothing up to ten per cent. This procedure is repeated with the occurrence of each pain. The use of the "mask" is just as effective as a nasal inhaler, but wastes more gas and so is more costly. When the head is passing the perineum the gas should be pushed to the point of anesthesia, while the patient's color will suggest the amount of oxygen to be used as well as serve to control the administration of the nitrous oxid. CHLOROFORM AND ETHER