in his own person the operation of tooth-extraction while rendered insensible by nitrous oxide. Satisfied, from further experience, that teeth could be extracted in this way without pain, Dr Wells proposed to establish the practice of painless dentistry under the influence of the gas; but in consequence of an unfortunate failure in an experiment at Boston he abandoned the project. On the 30th of September 1846 Dr W. T. G. Morton, a dentist of Boston, employed the vapour of ether to procure general anaesthesia in a case of tooth-extraction, and thereafter administered it in cases requiring surgical operation with complete success. This great achievement marked a new era in surgery. Operations were performed in America in numerous instances under ether inhalation, the result being only to establish more firmly its value as a successful anaesthetic. The news of the discovery reached England on the 17th of December 1846. On the 19th of December Mr Robinson, a dentist in London, and on the 21st Robert Liston, the eminent surgeon, operated on patients anesthetized by ether; and the practice soon became general both in Great Britain and on the continent.
Sir James Simpson was the first to apply anaesthesia by ether to midwifery practice; this he did in 1847, and found that the pains of labour could be abolished without interference with uterine contractions or injury to the child. On the 8th of March 1847 M. J. P. Flourens read a paper before the Académie des Sciences on the effect of chloroform on the lower animals, but no notice was taken of what has since proved to be a discovery of epoch-making importance. In November of the same year Simpson announced his discovery of the anaesthetic properties of chloroform, the trial of which had been suggested to him by Waldie, a chemist of Liverpool. As the result, chloroform came to be widely used instead of ether, though it was found by several casualties that it was not the absolutely safe anaesthetic that had at first been hoped. It, however, remained the drug that was chiefly used till Dr J. T. Clover (1825–1882) of London introduced his regulating ether-inhaler in 1876, embodying a new principle—that of limiting the quantity of air during etherization and regulating the strength of the vapour.
During the intervening period, as the results of the labours of John Snow, Sir Benjamin Ward Richardson, Thomas Nunnely, and Colton amongst others, several drugs were found to possess anaesthetic properties. Of these one, ethyl chloride, which was speedily given up, has come into deserved prominence at the present time; and another, nitrous oxide, which had been lost sight of since Wells’s failure at Boston, was reintroduced, and it became and has remained the most popular anaesthetic in dental practice.
Since 1876 no new drugs have been introduced; the progress has been in the direction of improvements in the technique of anaesthetization. The most important of these is the administration of oxygen with nitrous oxide, resulting from the recognition of the fact that this drug does not owe its anaesthetic properties to partial asphyxia, as was thought till the contrary was shown by Edmund Andrews of Chicago in 1868. It was not till twenty years later that this knowledge was put to practical use, when F. W. Hewett introduced his regulating stopcock, which enabled the anaesthetist to exhibit the nitrous oxide and oxygen in such proportions as were demanded by the patient’s condition. At the present time the anaesthetics in common use are the following:—
(1) Nitrous oxide gas, or laughing gas, N2O. This is a colourless, odourless gas, which for convenience is carried about in liquid form in iron cylinders. When about to be used, it is allowed to escape into a large rubber bag, connected with a closely-fitting face-piece, which covers up the nose and mouth, and allows of inspiration only from the bag of gas, expiration being into the air. When thus given the patient is exposed to a certain degree of asphyxia. This asphyxia is not only not necessary but is harmful, and may be obviated by giving oxygen in small amounts simultaneously by means of Hewett’s regulating stopcock. This drug is used chiefly for dental operations, and for minor surgery where absolute muscular relaxation is not required. When mixed with oxygen, it can be given if necessary for an hour or longer. It has an induction period of a few breaths only, and the recovery is as a rule unaccompanied by excitement or nausea. It is also used as a preliminary to ether; the gas is given till unconsciousness is reached, the unpleasant taste of the ether being thus avoided and the induction period shortened. The mortality from nitrous oxide is small, and from the gas and oxygen in expert hands nil.
(2) Ethyl chloride, C2H5Cl, a colourless liquid of a pleasant odour, boiling at 12·5° C. It is used in the same class of operations as the last anaesthetic. It is best given in an apparatus that consists of a mask closely adapted to the face, and a rubber bag of small capacity, with which is connected the bottle containing the ethyl chloride. The vapour supplied from the bottle is breathed backwards and forwards from the bag, fresh air being admitted in small quantities only. The period of induction is shorter than in the case of nitrous oxide, the patient losing consciousness in two or three breaths; the stage of recovery is not so uniformly pleasant, headache, nausea and vomiting occurring not infrequently. It is difficult at present to estimate the mortality, as it has only recently come into general use, but it seems to occupy an intermediate position between ether and chloroform.
(3) Ether, or ethyl oxide, (C2H5)2O, a colourless, volatile liquid, boiling at 36·5° C. It has a pungent odour. It is best administered, as in the case of ethyl chloride, by limiting the amount of air during inhalation. The induction is much slower than in the case of the last two drugs, and it is accompanied by a feeling of suffocation, owing to the pungent odour of the ether. On that account the anaesthetic is best started with nitrous oxide or ethyl chloride. The recovery is always marked by some nausea and very frequently by vomiting. The mortality is small during the actual operation, but fatalities from respiratory complications later on are not uncommon.
(4) Chloroform, CHCl3, a colourless liquid of a penetrating odour, boiling at 63° C. It is administered in such a way as to ensure the free admixture of air. To secure this the face-piece must be loosely-fitting, and the strength of the vapour so gradually increased that the patient is never inconvenienced or impelled to hold the breath. The induction is slow, occupying two or more minutes, but it is not at all unpleasant; nausea and vomiting during recovery are rarer than in the case of ether, but if they do occur they last longer. The mortality on the table is about 1 in 2500.
The question as to which is the better anaesthetic, ether or chloroform, for long operations, is a moot point. In the hands of an experienced anaesthetist there is probably nothing to choose as regards safety, and the anaesthetic advantages of the latter are incontestable. In the hands of the less-experienced anaesthetist, ether is the more suitable drug. At the extremes of life, chloroform is well taken, as it is also by women in labour, and it is indicated where there has been recent inflammation of the air passages. In operations, too, about the mouth, chloroform must be the drug used, as a closely-fitting mask is obviously impossible.
The introduction by inhalation of any of the above drugs into the organism produces an anaesthesia, the degree of which at any moment varies directly as the amount or tension of the vapour in the blood, and therefore also as the tension of the vapour in the inspired air. The organism in this case may be compared to an electric lamp, of which the voltage is, say 100, a current of any less voltage will only produce a red heat, however many amperes are forced through; with the voltage at 100 the filament will be white hot, at over 100 the filament will fuse. So with these drugs: with the vapour at a low tension a certain low depth of anaesthesia is obtained; if the administrator increases the tension, true surgical anaesthesia is produced; if he increases it again, the filament fuses and the patient dies. This is the principle which guides the anaesthetist; it is the quality of the vapour that decides the depth of the anaesthesia, not the quantity. An infinite quantity of chloroform may be absorbed with impunity if the tension be low, but a few drops will kill if the tension be high. For practical purposes four
