This section is from the book "Materia Medica And Therapeutics: An Introduction to the National Treatment of Disease", by John Mitchell Bruce. Also available from Amazon: The pharmacology and therapeutics of the materia medica.
The Vegetable Kingdom.
The Animal Kingdom.
Each article will be discussed under several distinct and definite headings, which are as follows: The names of the drug, in Latin and in English, its chemical formula, if any, and the definition of its nature; its source; its characters; its composition; its doses; and the preparations made from it.
A genera] reference must here be made to each of these headings.
Names, nature, and sources of drugs. - These are sufficiently indicated by the above plan in the case of the inorganic materia medica. It includes many of the chemical elements, and a great variety of compounds of the same.
Vegetable drugs are derived from entire plants, including fungi and lichens, stems (woods), green tops and twigs, roots and rhizomes, barks and leaves, buds, flowers, parts of flowers and flowering tops, fruits and seeds; and various vegetable products, including fixed and volatile oils, resins, oleo-resins, balsams, gums, gum-resins, inspissated juices and secretions. The animal materia medica includes entire animals, portions of animals, and products yielded either during life or after death.
The methods for obtaining the drugs will generally be given, and must be learned by the student, who should repeat for himself as many as possible of the easier processes. Most of these are already familiar to him in chemistry, such as solution, filtration, evaporation, crystallisation, precipitation, decantation, sublimation, distillation, destructive distillation, digestion, and washing. A few specially pharmaceutical processes will, however, require to be defined:
Pulverisation, the powdering of drugs, is done on a large scale in powerful drug-mills. On a small scale it may be done by simple trituration (triturare, to pound), or powdering in the dry state; by levigation (levigare, to make smooth or fine), or rubbing down with the aid of a little fluid, the resulting paste being afterwards dried; or by mediate pulverisation, in which some very hard substance or medium is mixed with the drug, in order to break up its substance thoroughly. Powdered drugs necessarily require sifting.
Elutriation (elutriare, from eluere, to wash out) consists in diffusing an insoluble powder in water, allowing only the heavier part to settle, and decanting the fluid; allowing this again to settle for a longer time, so as to deposit a second or finer size of powder, and again decanting; and repeating the operation indefinitely until an extreme degree of fineness has been reached.
Lixiviation (lix, a lye) is a process of washing an ash or crude mixture of solids, for the purpose of dissolving out the constituents in the form of a lye, or water impregnated with salts.
Maceration and Percolation are described under Tincturoe (page 15).
Characters. - This part of the description must be studied practically. Using the Manual as his guide, the student must examine specimens of drugs, and note respecting each article its general appearance to the eye, whether liquid, solid, crystalline, etc.; its colour, its weight, its smell, and its taste (if non-poisonous). If convenient, his examination of the drug should follow the pharmacopoeial account farther, and include the determination of its reaction; of its solubility in water, alcohol, ether, oils, etc.; and of the effects of heat on its volatility, fusibility, etc. Other important chemical properties, bearing on its pharmaceutical applications, may have to be studied, especially its incompatibility with other drugs, which prevents their combination in preparations. Along with the characters, in many instances, certain tests are given, which introduce the student to the subject of Impurities, and the methods of distinguishing substances so like each other as to be very readily confounded. Impurities may be the result of the imperfect selection, preservation, or preparation of drugs, including chemical decomposition of every kind; or of fraudulent adulteration. Similarity is, of course, a matter of accident, but may give rise to serious error.
The tests of purity applied to inorganic drugs are mainly such as are familiar to the student of chemistry; and to avoid constant repetition, the most common of them will be represented here once for all:
Impurities derived from the sources of the drug, or formed in the process of manufac-ture and imperfectly removed.
Bibulous paper; dampness; loss of weight by heat.
White precipitate with BaCl2
White precipitate with AgNO3.
Yellow precipitate with AgNO3, soluble in HNO3 and in NH4HO.
Precipitate with lime-water; effervesces with acids.
Zinc and HC1 yield H1S.
H1SO4 and FeSO4 give a brown ring between the two fluids.
White precipitate with oxalate of ammonia or with
Yellow precipitate with II
Impurities derived from the apparatus used.
Precipitates with (NH4)2S, or H1S; and special tests.
Various colored earths.
Non-volatility; insolubility in HNO3.
Blue colour with iodine.
Evaporation; quantitative test.
In the case of organic drugs, impurities are chiefly to be detected by careful physical examination and special quantitative tests.
Composition. - The composition of the inorganic drugs is expressed by their name and formula. On the other hand, the organic drugs are frequently highly complex, the chief proximate principles being the following: Fixed oils, volatile oils, resins, oleo-resins, gums, gum-resins, balsams, pectin, alkaloids, acids, neutral substances, glucosides, starch, sugar, cellulose, albuminous substances, ferments, colouring matter, salts, and extractives. Some of these demand general consideration.
Fixed oils are extracted by expression (if possible, without the aid of heat) from the seeds or fruits of plants, or from animal tissues. They are composed of oleate, with palmitate and stearate of glyceryl; that is, are compounds of fatty acids (oleic, palmitic, and stearic, as well as of other, less common) with the radical glyceryl, C3H5. With caustic alkalies or metallic oxides, they form soaps, the metal displacing the glyceryl, which is hydrated, and becomes glycerine, C3H53HO.
Volatile Oils; Resins; Oleo-resins; Balsams. - Volatile oils are obtained by distillation from entire plants, flowers, fruits, or seeds. Most of them are colourless when pure, and highly aromatic. They consist of a liquid hydrocarbon or eloeopten, generally isomeric or identical with terpene, the hydrocarbon of oil of turpentine, C10H16; and of an oxydised hydrocarbon, usually a solid body, or stearopten, like camphor, C10H16O. A few volatile oils contain sulphur and nitrogen. Further oxydation converts a portion of volatile oils into resins, solid, brittle, nonvolatile bodies, and thus gives rise to oleo-resins, which can be broken up into their two constituents by distillation. Resins or oleo-resins yielding benzoic or cinnamic acids are called balsams.