The absolute beginner may be so completely out of his reckoning as to mistake the quietude of the later part of the first stage for the appearance of the third stage. For the prevention of so gross an error as that, the reader need only be referred to a patient study of the foregoing. But even a man with considerable experience may frequently be in doubt exactly as to _how far through the third stage his patient has passed_. He may have attained a level which will permit an incision to be made into the skin without movement on the part of the patient, but not one which would relax the abdominal muscles sufficiently for the peritoneum to be opened without eliciting considerable resistance from the abdominal muscles. In such moments of doubt, the author is accustomed to request the surgeon to make his skin incision, and _observe the effect which this trauma has upon the depth, frequency, and regularity of respiration_. This furnishes a most valuable guide to the depth of anæsthesia. In a third stage of very light degree, the respiratory rhythm will be interrupted and the breath held for a second in inspiration. Apart from any other sign, that may be taken as an index that the anæsthesia is very light--too light to permit of opening the peritoneal cavity. In a very deep anæsthesia the respiration is little affected by the skin incision, while at a moderate and more desirable level the respiration is quickened and deepened, but unaffected in the regularity of its rhythm. THE FOURTH STAGE IS STAGE OF OVER-DOSE.--This stage is, of course, never entered voluntarily. Its earliest signs are loss of all tone in the muscles of expression, complete loss of corneal reflex, a widely dilated pupil _insensitive to light_, and a type of respiration which though definitely weakened may show occasional deep gasps. Circulatory failure and cessation of respiration from failure of the medullary centre are the closing phenomena of overdose. The Circulation in Anæsthesia. It will be perhaps noticed that in the foregoing, no reference has been made to the examination of the pulse. This is not an oversight on the part of the author. It is perfectly true that under any anæsthetic not complicated by an asphysical element, the blood pressure falls as the drug takes effect, and that in the case of chloroform the fall is often quite considerable. Such a fall can be appreciated by the skilled finger, but only by concentrating upon that examination a degree of attention which necessarily detracts from the administrator’s available energy for the observation of other signs which are of equal value, and can be more rapidly and certainly appreciated and appraised.