_In the first stage_ there is struggling and excitement, due partly to the action of the drug and partly to fright. The local irritant action of the vapor causes choking and coughing, which also induces struggling. The respiratory and cardiac centers are temporarily stimulated, as a consequence of which the pulse and respiratory movements are increased in force and frequency and blood tension is raised. The smaller animals, particularly the dog, may vomit during the first stage of anaesthesia. In the first stage the dog may bark, whine or howl, the horse neighs and groans; other animals give expression to sounds more or less characteristic to their species. _The second or anesthetic stage_ is characterized by loss of consciousness, sensation, motion and partial loss of reflex action and is that state suitable for operations. The stimulating action of the anesthetic has passed and there is now depression of the cerebral functions, the motor centers. The voluntary muscles are completely relaxed, the sphincters occasionally, the patient lies absolutely motionless, the cornea fails to respond to irritation, i. e., winking is not produced when the cornea is lightly touched with the finger. Sometimes the muscles are rigid and twitching during this stage of anesthesia, though sensation and consciousness are absent. In the anesthesia stage the pulse is slow, full and strong, due to lowered blood pressure, the breathing is slow and shallow but regular. _The third or paralytic stage_, which must be carefully watched against, poisoning is beginning and there is depression of the three great medullary centers controlling the heart, respiration and vascular tension and also the posterior reflex centers of the spinal cord, so that the urine and faeces are passed involuntarily. The passage of urine frequently occurs in the first stages of anesthesia and should not of itself be considered a danger mark. When the pulse becomes rapid, feeble and irregular, the breathing is at first stertorous and then the respiratory movements become shallow and weak, with long intervals intervening between them; this irregularity is a most important danger sign. The skin and mucous membrane often become cold and clammy. The pupils are usually widely dilated, though death may occur with either dilated or contracted pupils and consequently no dependence should be put in this sign unless there has been a sudden change from one condition of the pupils to the other. The three above mentioned stages are conventional, and are not in any case so clearly defined in practice as they are described theoretically upon paper. The first stage may be either absent or prolonged, and the last stage should not be reached at all. COMPARISON OF ETHER WITH CHLOROFORM