When first introduced, it was expected by enthusiasts that the lightness and portability of the drug itself and of the necessary inhaler, would enable ethyl chloride to oust nitrous oxide from its recognised place in surgery and dentistry. These high expectations have for several reasons not been fulfilled. In the first place, this drug is essentially a “single dose” anæsthetic. Most authorities view coldly all attempts to prolong anæsthesia by repeated or continued administration. Secondly, ethyl chloride has a mortality rate very much greater than nitrous oxide if doses sufficient in themselves to produce anæsthesia are habitually used (_vide supra_). The introduction of the “vapour” method has done much to mitigate the risks, but even then, this anæsthetic cannot approach the high level of safety rightly credited to N_{2}O. Moreover, it leads to after vomiting much more commonly than its rival. In many schools these considerations have been held so powerful that ethyl chloride has been entirely abandoned. It is, however, a very valuable drug for the following purposes:-- (1) The removal of tonsils and adenoids. For this operation, the speed with which the patient (usually a child) loses consciousness, the pleasant type of anæsthesia and absence of all serious asphyxial phenomena, and the rapid re-appearance of the cough reflex when once the inhaler is removed, are all strong recommendations. (2) As an adjuvant to gas, or gas oxygen (_see_ Chapter XIII.). (3) As a help to the speedy and comfortable induction of “closed ether” (_see_ Chapter XV.). CHAPTER XIII. MIXTURES OF NITROUS OXIDE AND ETHYL CHLORIDE. Dr Guy, Dean of the Edinburgh Dental School, introduced some years ago a method of giving ethyl chloride in mixture with nitrous oxide. Guy’s objective was to utilise the many excellent features of the drug without incurring the risks which are apparently inherent in it when a dose sufficient in itself to induce full narcosis is used. Given in mixture with gas, a much smaller dose suffices. [Illustration: FIG. 42.--Guy’s inhaler for N_{2}O and Ethyl Chloride.] His original apparatus is shown in Fig. 42, the details are shown in Fig. 43. The horizontal limb of a 3-way gas tap is prolonged half an inch. In each side of the prolongation is a hole. The bag mount has in its side also one hole, which is connected by a universal ball and socket joint, with the rubber tube to which the ethyl chloride vial is attached. An indicator on the outside of the bag mount and a mark upon the outside of the horizontal limb of the 3-way tap, serve by their apposition or the reverse to show whether the ethyl chloride vial is in direct continuity with the interior of the inhaler. For purposes of description, Dr Guy calls these two positions, “in register” and “out of register.”