Cocaine, owing to the unsatisfactory results which have attended its use as a topical application, is now generally applied by hypodermic injection, for the extraction of teeth. Owing to the necessity for introducing the agent deeply into the tissues, Dr. Walb's method is to inject a two per cent. solution of the hydrochlorate of cocaine hypodermically over the root of the tooth to be extracted, the injections being usually made on each side of the gum, above the root of the tooth, and as many as the number of teeth to be extracted may indicate; the same method is employed for obtunding hypersensitive dentine, and in removing pulps. The full anaesthetic effect is developed in from five to ten minutes, and continues ten or fifteen minutes. It has also been suggested to hypodermically inject the solutions of cocaine upon both the lingual branch and the inferior dental branch of the inferior maxillary nerve, the former being preferred by some, on account of its supplying the alveoli and gums; but greater success appears to result from injecting the gum on each side of the tooth. Dr. Raymond recommends charging the syringe with thirteen minims of a four per cent. solution of cocaine, and to direct the needle-point on a line extending about midway between the angle and the coronoid process of the inferior maxillary, passing through the internal pterygoid muscle, and, using the finger on the external oblique line as a guide, to carry the needle point along inner surface of ramus until the nerve is reached, where it enters the inferior dental foramen, for operations on the inferior molar teeth.

Dr. Raymond also suggests the following method of preparing and applying cocaine: Obtain a quantity of the soluble alkaloid, and mix it at the time of using it (as it deteriorates when long kept). The requisites are a minim glass, pair of scales, some filtering paper, and a little water that has been boiled. It is necessary to have an easy-working syringe, with a perfectly smooth, sharp needle. Care must be taken to exhaust the air from the syringe when charged ready for use. This can be done by drawing in more of the solution than is needed, and pressing it out to the required number of minims. Hold the needle point up, so as to allow the air to get above the solution, then press the piston.

The needle of the hypodermic syringe should be fine, sharp and clean, and rendered thoroughly aseptic previous to its employment, which may be accomplished by drawing up through it a few drops of any good antiseptic solution, such as strong carbolic acid, and the solution should be freshly prepared for each operation as the salts of cocaine rapidly decompose; or the needle of the syringe can be immersed in, and the barrel filled with, boiling water rendered alkaline by the addition of a small quantity of bicarbonate of soda. The salt should be dissolved in slightly warm water, and the strength of the solution vary from 5 to 20 per cent. A five per cent solution is made by dissolving 1/2 grain of cocaine in 10 minims of water. Previous to the injection, the gum should be dried about the tooth, and a folded napkin so placed as to exclude the saliva. All air must be expelled from the syringe, and the gum at the point the needle of syringe is to enter, should be obtunded by applying a few drops of the solution to the mucous membrane, so as to render the puncture painless. It is recommended to inject the solution at three points, two punctures on the labial or buccal surface, and one on the palatine or lingual surface. The point of the needle should be inserted about one-sixth of an inch below the free margin of the gum, and pressed in obliquely, upwards or downwards, as the case may be, in a direction towards the apex of the tooth, until the point of the needle rests against the bone; all of the soft tissues must be penetrated. With the needle in position, and a finger placed on either side and pressed with some force against the gum to keep the tissues in place, the solution should be slowly injected, when the gum should appear completely blanched in the neighborhood of the puncture. After injecting the solution the needle should not be withdrawn for several seconds, and then a finger should be placed over the puncture to prevent any escape of the solution. Some six or seven minutes elapse before the full anaesthetic effects of the cocaine are obtained. Dr. Gask recommends placing a few crystals of the salt just around the neck of the tooth to render painless the application of the forceps, and he prefers for injection hydrochlorate of cocaine in the form of half-grain tabloids. Rinsing the mouth with hot water before the injection of cocaine solution, and again afterwards, and repeating the injection, is a method which is attended with satisfactory results.

The best syringe for hypodermic use consists of one made altogether of metal with no leather packing as this is unclean. The metal piston is accurately ground to fit the metal barrel, and the piston should be touched with glycerine before using the syringe, as this is easily washed off. Such a syringe can be boiled without the slightest injury, which should be done every time it is used.

The combined use of cocaine and chloroform is advocated by Obolinski, who injects, either before or after the anaesthesia is obtained, from one to three centigrammes of cocaine ; or he injects in the neighborhood of the seat of operation, and during its progress, from three to seven centigrammes. Cocaine is thus used on the ground that it is a complete antagonist to chloroform, of which, however, there is some doubt, as cocaine is rather a general excitant of the central nervous gray matter than a direct and powerful stimulator of the heart, while its stimulant effect upon respiration is not to be depended upon. Obolinski claims that this mixed narcosis requires the use of less chloroform, that vomiting is prevented, and that there are few disagreeable aftereffects. Dr. Gordon White recommends a saturated solution of cocaine hydrochlorate in ether as an excellent preparation for sensitive dentine and pulp-extirpation. (See Vapocaine.) A mixture of cocaine and guaiacol in crystalline form, made into a thick paste, is recommended for hypersensitive dentine.