“SINGLE DOSE” methods are of use chiefly in dental surgery. The patient is charged up with the anæsthetic, and the operator has to begin his work as soon as the mask is withdrawn from the face, ceasing as soon as the patient shows any signs of recovering consciousness of pain. Single dose anæsthetics are in a class by themselves. In order to achieve success with them, special experience on the part of the administrator and mutual confidence between operator and anæsthetist are essential. The period of anæsthesia available to the operator which any particular “single dose” anæsthetic may be expected to yield is obviously a matter of the first importance, and the table given in Chapter XIX. will be found helpful in this connection. CHAPTER V. THE CLINICAL OBSERVATION OF THE PATIENT. Stages of Anæsthesia. Anæsthesia has been divided into four clinical stages corresponding to the degrees to which the nervous system has been affected. The boundaries between these stages are often ill-defined, but the terminology has some value as facilitating description. THE FIRST STAGE lasts from the commencement of inhalation up to the time when volitional self-control is lost by the patient. THE SECOND STAGE in the older text-books was said to be characterised by struggling, shouting, and breath-holding. With a patient not addicted to alcohol and with the anæsthetic skilfully administered, this description is unduly lurid. THE THIRD STAGE is that of full surgical anæsthesia. THE FOURTH STAGE is that of over-dosage. The Ocular Reflexes in Anæsthesia. These give such valuable assistance to the anæsthetist that it will be well to define and describe them as a preliminary. They are three in number. THE CONJUNCTIVAL REFLEX is best elicited by drawing the upper lid upwards from the eyeball and retaining it in that position with one finger, while with another finger the ocular conjunctiva is lightly touched in the area of the inner canthus. If the anæsthesia is very light, both lids attempt to approximate and close the palebral fissure. The upper lid may slip down from under the retaining finger and come into its proper place, while the lower lid is elevated. At a deeper level of anæsthesia there is not complete action of the orbicularis but merely of a certain part of it, so that all that is observed is a _twitch inwards of the lower lid_. Even this form of the reflex disappears before the corneal reflex.