This is intended to protect pills so that they may pass the stomach undissolved, the keratin being insoluble in the gastric juice, but soluble in the alkaline contents of the intestines. Only fatty excipients (such as kaolin ointment) should be used in massing, and the pills should be covered with a thin layer of cocoa-butter previous to applying the keratin solution. This solution is made from horn shavings, which are first macerated in ether to remove fat, then dried. Next the shavings are digested for several days in a solution of pepsin 4 parts, hydrochloric acid 1 part, and water 95 parts. All that remains undigested is washed, and dissolved in solution of ammonia or acetic acid, and evaporated until only a trace of the solvent is left. The gum-like liquid which remains is the coating-solution, and several thin coats of this are imparted to the pills. The process is troublesome, and not a success, as the coating becomes sticky and nasty.