ANAESTHESIA and ANAESTHETICS, terms used in medicine to describe a state of local or general insensibility to external impressions, and the substances used for inducing this state. In diseases of the brain or spinal cord anaesthesia is an occasional symptom, but in such cases it is usually limited in extent, involving a limb or a definite area of the body's surface and depends upon interference with nerve tracts or centres. Complete anaesthesia occurs in a state of catalepsy or trance.
On April 9, 1799, Sir Humphry Davy, while experimenting on nitrous oxide (the so-called "laughing gas"), discovered its anaesthetic properties, and described the effects it had on himself when inhaled with the view of relieving local pain. In 1818 Faraday showed that the inhalation of the vapour of ether pro duced similar anaesthetic effects, as was also shown by the Ameri can, John D. Godman (1822), James Jackson (1833), Wood and Bache (1834) . These observations, in spite of the work of Henry Hickman in his famous pamphlet "A Letter on Suspended Animation" in 1824, remained scientific curiosities until March 3o, 1842, when Dr. Crawford D. Long performed at Jefferson, Ga., an operation under ether. His statue now stands in the statu ary hall in the Capitol, Washington, D.C. In December 1844 Dr. Horace Wells, a dentist of Hartford (Conn.), underwent in his own person the operation of tooth-extraction while rendered in sensible by nitrous oxide. On Sept. 3o, 1846, Dr. W. T. G. Morton, a dentist of Boston, following the suggestion of Dr. C. T. Jackson, employed the vapour of ether in private to procure general anaesthesia in a case of tooth-extraction, and thereafter admin istered it in cases requiring surgical operation with complete suc cess. The first operation in public under ether was performed by Dr. J. C. Warren at the Massachusetts General Hospital on Oct. 16, 1846. On Dec. 19 of the same year Robinson, a dentist in London, and on the 21 st Robert Liston, the eminent surgeon, oper ated on patients anaesthetized by ether; and the practice soon became general both in Great Britain and on the continent.
Sir James Simpson, in 1847, was the first to apply anaesthesia by ether to midwifery practice. On March 8, 1847, M. J. P. Flourens read a paper before the Academie des Sciences on the effect of chloroform on lower animals, and in November of the same year Simpson announced his discovery of the anaesthetic properties of chloroform. During the intervening period other drugs were found to possess anaesthetic properties. Of these ethyl chloride has come into prominence at the present time ; nitrous oxide, too, which had been lost sight of, was reintroduced, to become the most popular anaesthetic in dental practice. Frequently, either alone or with oxygen, nitrous oxide is used in the preliminary stages of inducing ether anaesthesia.
The administration of the above-named drugs is by inhalation, and has to be continued throughout the operation, the reason being that all the drugs are as rapidly excreted as they are absorbed, especially by the lungs, and therefore no other method would be of any avail. On the other hand there are drugs which are suffi ciently slowly eliminated to allow of an operation being performed between the moment of induction and that of recovery. The use of scopolamine and morphine in the production of "twilight sleep" for childbirth is an example. These drugs are injected with a hypo dermic needle. Similarly, urethane produces a profound general anaesthesia but has only been used on the lower animals, as its depressing effect on the respiratory centre contra-indicates its use in human beings.