Although this is a pharmacopceial article no pharmacist may undertake its preparation without first obtaining the sanction of the Home Office. Permission is not at all likely to be obtained. A 10-per-cent. alcoholic solution can be purchased from wholesale houses.

Physostigmine Salts and their solutions become red on exposure to the air, through formation of rubeserine owing to action of ammonia in the atmosphere. A mere trace of hypophosphorous acid added to the solutions (a single drop of 10-per-cent. acid to the ounce) prevents the change of colour. Extract of Calabar bean is sometimes prescribed in aqueous solution. This should have 1 grain of salicylic acid added to each ounce, and should be filtered, as the water-insoluble matter is merely fat and resin, which would irritate the eye.