A highly inflammable gas at the ordinary room temperature, it must never be used near a fire. It may easily be liquefied, and is used both as a general and a local anaesthetic. In obstetrics and in dentistry it may take the place of chloroform or of nitrous oxide, and it may be used preliminary to the administration of ether or chloroform. The liquid comes in sealed glass tubes with capillary points which are to be broken off or unscrewed when the liquid is volatilized by the warmth of the hand. The stream is directed upon the point desired in local anaesthesia, the tube being held a few inches away. Anaesthesia is usually effected in fifteen to twenty seconds. It should not be applied so long that the tissues are frozen hard, but should be removed as soon as they appear white. Too much freezing may cause delayed healing or a slough.