This section is from the book "Dental Medicine. A Manual Of Dental Materia Medica And Therapeutics", by Ferdinand J. S. Gorgas. Also available from Amazon: Dental Medicine.
Chloride of Methyl is produced by the action of chlorine upon marsh gas; by heating together common salt, sulphuric acid and methyl alcohol; or it is more cheaply manufactured by using the waste products of beets used in the manufacture of sugar. It is the chloride of a hydrocarbon in the form of methyl chloride, and resembles ether in appearance, taste and smell, but is less inflammable. Chloride of Methyl is generally employed as a local anaesthetic in the form of spray, although it possesses general anaesthetic properties also, and being very volatile and ether-like, rapid evaporation occurs when it is applied over an effected area. To avoid producing inflammation of the skin, or an erythema in persons having an irritable skin, caution is necessary; and it should be applied over as many nerve filaments as possible. The special advantage of chloride of methyl is its external application, which may never cause more than a temporary irritation of the skin. In order to produce local anaesthesia with this agent, M. Bardet proposes before spraying a surface with it, to paint it with glycerine, the revulsive action being less severe, and the glycerine forming a surface on which the drops of the refrigerant mixture collect, and which may be readily removed after the desired effect has been produced ; the use of glycerine is also said to prevent the dangers of sloughing. Dr. Ch. Bailly recommends the following method of applying this agent as a local anaesthetic: A tampon of dry cotton covered with dry silk is sprayed with the anaesthetic until its temperature is reduced to 23°-55° C. below zero. The tampon is then grasped with ebony pincers and applied for a few seconds to the parts to be anaesthetized, and perfect abolition of pain at once secured. Drs. Daboll and Rhein recommend chloride of methyl as an application for trigeminal neuralgia, giving immediate relief by paralyzing the small filaments of the nerve. The spray is also used for obtunding sensitive dentine; it produces a more intense cold than ether, and with less pain, its obtunding effect lasting a longer time.