Keratinum. Keratin.
Keratin is a protein substance, which forms the chief part of horns, hoofs, feathers, wool, etc. It contains the elements carbon, hydrogen, oxygen, nitrogen, and sulphur, the latter being in very loose combination, and in variable proportions. Keratin may be obtained by macerating horn shavings for some days in a mixture of equal parts of ether and alcohol, decanting the liquid, and washing the residue with warm water. The washed shavings are then treated for some hours with an acidified solution of pepsin at 40°. After further washing with distilled water, the residue is dried and powdered. It may be further purified, by boiling with glacial acetic acid for about thirty hours, in a flask fitted with a reflux condenser, filtering the solution thus obtained through glass wool, and evaporating it to a thick syrupy consistence, after which it may be spread on glass plates, dried between 60° and 70°, and scaled. Keratin occurs as a brownish-yellow powder, or in transparent, white, or greyish-white, scales, without taste or odour. It may be softened by long boiling in water, and is decomposed by boiling under pressure, a turbid solution being formed, and hydrogen sulphide liberated. Boiling with diluted sulphuric acid converts it into leucine, tyrosine, and other products. On burning keratin, an odour resembling that of burnt feathers is evolved, and the carbon remaining is very difficult to incinerate. On complete combustion it should not leave more than 1 per cent. of ash. After twenty-four hours' digestion with fifteen times its volume of solution of ammonia or glacial acetic acid, at 25° to 40°, keratin should not leave more than 3 per cent. of insoluble residue.
Soluble in concentrated acetic acid, caustic alkalies, or ammonia; insoluble in water, alcohol, ether, diluted acetic acid, or acid pepsin solutions.
Uses.—Keratin is used in pharmacy mainly for the purpose of coating pills, tablets, and capsules that are required to pass through the stomach unchanged, in order that the contents may exert their action only in the intestines. Considerable doubt exists regarding the efficiency of keratin for this purpose (see Keratin Coating).
PREPARATION.
- Liquor Keratini, B.P.C.—SOLUTION OF KERATIN. 1 in 10.
- Used as a coating for pills which are intended to pass through the stomach and act in the small intestine; they should first be thinly coated with oil of theobroma, then twice with keratin solution, and finally varnished with sandarac. Pills which are to be coated with keratin should be massed with an oily excipient. A much more elegant, expeditious, and trustworthy method of preparing drugs for intestinal solution is to enclose the mass in gelatin capsules, and render the latter insoluble in the gastric secretion by dipping them in solution of formaldehyde. They are then known as "Glutoid" capsules. (See Capsulae.) They are capable of expansion without rupture, and their contents are therefore less liable to become exposed in the stomach than are those of a keratin-coated pill or tablet.
