An anaesthetic is a drug which reduces sensation.

A brief history of anaesthetics:-
Of the few anaesthetic agents known to the ancients, opium and hemp were the most important. Both were taken by ingestion or by burning the drug and inhaling the smoke. Nitrous oxide ,discovered by the British chemist Sir Humphry Davy about 1800, was first used as anaesthetic in 1844 by American dentist Horace Wells. In 1842 the American surgeon Crawford Long successfully used ethyl ether as a general anaesthetic during general surgery. He failed to publish his findings however and the credit for the discovery of the anaesthetic properties of ether was given to the American dentist William Morton, who in 1846 publically demostrated it's use during a tooth extraction. In 1847 the British physician Sir James Simpson discovered the anaesthetic properties of chloroform. Many other general anaesthetics have since been discovered. Ether and chloroform have been largely abandoned because of their dangerous side affects and flammability. Some anaesthetics work by depressing the central nervous system, whereas others induce amnesia and dissociation.

Basically anaesthetics come in two major forms:-
(1) Local Anaesthetics - This type only affect a specific area of the body and usually leave the patient fully awake and alert.
(2) General anaesthetics - This type affect the whole body resulting in a loss of conciousness meaning the patient has no awareness of what is going on.

Local Anaesthetics.

Local anaesthetics are used in most areas of medicine from the dentists chair to the chiropodists table.
They work by temporarily blocking the nerve condition without damaging the nerve fibres. Local anaesthesia is produced by injecting into the tissues affected a soloution of a natural alkaloid such as cocaine, the oldest of all anaesthetics, or a synthetic agent such as procaine,widely known under it's trade names of Novocaine, Lidocaine and Xylocaine.

Block anaesthesia, a much more extensive aneasthesia, is produced by injecting the agent into a nerve trunk, next to a nerve, or all around the operative field, thereby deadening the entire area.The best known block anaesthesia is probably the spinal block, produced by injecting an anaesthetic into the spinal canal.

A mild local anaesthesia, useful in minor dental and medical procedures, can be produced by numbing the tissues with cold, either by applying ice or by spraying with a volatile liquid such as ethyl chloride.
The use of a local anesthetic, rather than a general one, is required when the proceedure does not need total muscle relaxation. The nerve passage is temporarily blocked, rather than damaging the nerve fibres The local anesthesia is provided by injection to the tissues of either a natural alkaloid solution, or a synthetic agent such as Procaine .

. Procaine Hydrochloride (Novocain) as an anaesthetic.

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