Local Anæsthetics

Local anæsthesia, already alluded to as probably the earliest form of numbing sensibility to pain, was practised in antient times by the inunction of various narcotics, but after the seventeenth century the practice seems to have almost entirely gone out of use. The latter end of the nineteenth century, however, marks a new era in this department.

On September 15th, 1884, considerable interest was aroused by a communication made at the Ophthalmological Congress at Heidelberg, by Karl Koller, of Vienna, in which he demonstrated the effects of cocaine as a local anæsthetic.

The discovery of Cocaine

The alkaloid now known as cocaine was isolated by Gädeke, from the leaves of the Erythroxylon Coca as far back as 1855. He called it ethroxylene. Four years later a further investigation of the plant was made by Nieman, who noticed that the leaves produced a numbness of the tongue; and in 1874 Hughes Bennett demonstrated that cocaine possessed anæsthetic properties. In 1880, Von Anrep, who made a careful investigation of the drug, hinted that the alkaloid might be of use in general surgery as a local anæsthetic, and Koller undertook a series of experiments on animals in the laboratory of Professor Stricker, in which he found that complete anæsthesia of the eye, lasting, on an average, ten minutes, followed the introduction of a two per cent. solution of the alkaloid.

The immense value of such an anæsthetic in ophthalmic operations was universally recognised, and it at once came into general use. In painful conditions of mucous surfaces, and for minor operations, cocaine has been found of great service, and as a local anæsthetic it has a large field of usefulness. Since the introduction of cocaine, other substances have been brought forward, which, after extensive trials, have proved to be of real clinical value. Of these may be mentioned eucaine, a synthetic product (benzoyl-vinyl-diaceton-alkamine) discovered by Merling, and first studied by Vinci in Liebreich’s laboratory. Of the two forms of this drug used, which are known as A and B, the latter was soon found to be the only one suitable for producing local anæsthesia. Its properties are similar to those of cocaine, with the exception that it produces no vaso-constriction, and it is claimed that it is equal in anæsthetic power, whilst its toxicity is very much less.

Stovaine and Tropa-cocaine

Stovaine, or benzoyl-ethyl-dimethylaminopropanol hydro­chloride, more recently introduced, is a synthetic product elaborated by Fourneau, and derived from tertiary amyl alcohol. It is much less toxic than cocaine, but its comparative value still remains to be proved by further trial. Tropa-cocaine, a drug closely allied to cocaine, and derived from the leaves of the Java coca plant, has recently been much used in Germany, but it does not appear to possess any advantages over cocaine or eucaine.

Novocaine, or para-amido-benzoyl-diethylamino-ethenol hydro­chloride, has lately been found to possess satisfactory properties as a local anæsthetic in dental operations. It is said to be free from the toxic and local irritant action common to other local anæsthetics.