It is wise, particularly in one’s early days, to give a trace of ether vapour during the latter part of the induction stage, and to maintain it until the operation is well under way. Once the anæsthetist is satisfied that the narcosis is proving deep enough for the purposes of the operation, the ether may be shut off and will probably not be required again. Remember that _depth_ of anæsthesia can be secured in three ways--(1) cutting down the oxygen percentage; (2) increasing the tension of the mixed gases; (3) adding a little ether. Of these, No. 1 is most undesirable, and if carried to the least excess over a period of more than a minute or two may lead to an accident. No. 3 is the means for the beginner to rely upon, until he learns the judicious and skilful use of No 2. The anæsthetist who is learning the method of anæsthesing must resolve that nothing shall tempt him to overstep the stage of dull pink colour, and moderate pupils. If with gas-oxygen alone, he cannot get a satisfactory anæsthesia without resorting to oxygen starvation, let him not be ashamed to turn on his ether. Abdominal relaxation sufficiently complete to permit the surgeon to explore the abdominal cavity with ease, is not readily secured by gas-oxygen in a patient of robust type. Fortunately, it is the weakly or the severely shocked who really _need_ this form of anæsthesia, and in them abdominal relaxation is fairly easily obtained. Professor Crile, as has already been explained, does not rely upon the inhalational anæsthetic alone. He infiltrates each layer of the parietes with novocain, thus producing a local anæsthesia. If this method be faithfully carried out by the surgeon, a most complete relaxation of the muscles can be secured. CHAPTER IX. ETHER. The drug commonly known as ether and otherwise described as ethylic ether or sulphuric ether, has a chemical formula (C_{2}H_{5})_{2}O. It is a transparent colourless fluid with a specific gravity of ·720 to ·723. A brand much used in the States has an S.G. of ·713 only, a point which is greatly emphasised by its supporters, who claim that it volatises quicker and therefore is more powerful in action. The author has in actual practise not found much difference between this brand and any good British one. Ether is highly inflammable and volatilises readily at ordinary room temperatures. Its boiling point is 96° to 98° Fahr. Whether evaporating from a fabric such as gauze, or from bulk in a jar, ether cools very rapidly, and the fall in temperature soon reduces the ease of its volatisation. This point is of some practical importance in anæsthetics, and some years ago the author made a number of observations, hitherto unpublished, with a view of ascertaining some definite facts in this connection. His results will be found in Appendix I.