Preparation. - Horn-turnings are digested with artificial gastric juice until all the matter soluble in them has been removed. They are then allowed to lie for some weeks in ammonia or glacial acetic acid, which gradually dissolves them. The solvent is then allowed gradually to evaporate until a mucilaginous solution is obtained.

Characters. - The solution resembles gum in appearance, and when dry forms yellow or yellowish-brown scales. When dried, keratin is absolutely insoluble in gastric juice, but dissolves readily in the juices of the intestine.

Uses. - To coat pills containing any substance which we wish to act upon the intestine without acting on the stomach. These are: 1. Such substances as irritate the gastric mucous membrane when long used, e.g. arsenic, all anthelmintics, salicylic acid, creasote, chrysarobin, copaiba, cubebs, digitalis, preparations of iron (and especially the iodide and chloride), preparations of mercury (especially the perchloride and periodide), opium, phosphorus, quinine, tartarated antimony.

2. Such substances as impair digestion in the stomach by forming insoluble precipitates with pepsin and peptones, e.g. tannic acid, alum, acetate of lead, subnitrate of bismuth, nitrate of silver, corrosive sublimate.

3. Such substances as are partly rendered inert by the gastric juice, and partly decomposed in an undesired manner, e.g. alkalis, soap, bile, calcium sulphide, ferric sulphide, charcoal, nitrate of silver, iodide of iron, green and red iodides of mercury, etc.

4. Medicines which we wish to introduce into the duodenum in as concentrated a form as possible, e.g. kousso, extract of male fern, santonin, nitrate of silver, acetate of lead or tannin in ulceration of the bowels, bile, charcoal, soaps, and alkalis, etc.

5. Medicines of which we desire the remote without the local action, e.g. iron, quinine, arsenic in gastric catarrh, in anaemia, in cardialgia and gastric ulcer.

Mode of Application. - The medicine is thoroughly mixed with marsh-mallow powder, liquorice powder, or charcoal, and a few drops of almond oil. It is then made into a pill-mass with cacao-butter. After the pills have been made of the proper size they are covered with a thin coating of cacao-butter, and then with one, or better still with two or three coats of keratin.

Usually the solution of keratin in ammonia is employed, but the solvent least likely to decompose the medicine may be employed, and thus the acetic acid solution may be used for the chloride of iron or mercury, or salicylic acid.