Nothing has yet proved of such general usefulness as this invention of the late Mr. Barnard Proctor, the Newcastle-on-Tyne pharmacist. The original formula differed slightly from that in the British Pharmacopoeia, being as follows:

Mix the gum and glycerin till smooth before adding the water.

Mr. Proctor remarked of this:'Four ounces of the dry materials require exactly 1 ounce of this mucilage to form a convenient mass, which retains its plastic condition, its solubility, its retentiveness of shape, and a ready miscibility with other aqueous masses, if that were necessary.'The glycerin is the best excipient for salts and metallic oxides, such as potassium bromide and bismuth subnitrate. The mass should be well kneaded, or more of the excipient will be used than is really necessary. This may be remedied by the cautious addition of a little glycerin and water to the pill-ingredients.

Water is a vehicle rather than an excipient. It is used along with substances which contain within themselves a binding material, such as gum, or in masses containing soap. As a rule 3 minims of water suffices for a dozen 5 -grain pills.

Wax or Cocoa Butter is useful to thicken essential oils and the like before kneading them into a mass with powdered althaea. Melt the wax or cocoa butter in a pill-tube by a gentle heat, add the oil, stir, and mass with the powder- 1 grain of wax for 2 minims of oil. Cocoa butter is excellent as an excipient for oxidising-substances- e.g., silver oxide.