Page:A manual of pharmacology and its applications to therapeutics and toxicology (1922).djvu/19

18 Flowers (Flores).—Chamomile, Arnica. Unexpanded flowers are: Cloves, Santonica.

Fruit (Fructus).—The ripened ovary, with any persistent parts of the flower, and containing the seeds (Pepper, Cardamom, Hops, Colocynth, Anise).

Seed (Semen).—The essential part of the fruit (Nux Vomica, Strophanthus, Physostigma, Mustard, Linseed). Microscopic Structure of Plants.—This differs from the animal cells, especially by the thick cell walls, and by the frequent presence of protoplasmic enclosures, starch, fats, calcium oxalate, protein crystals, etc. The cell walls are chiefly responsible for the shape and physical properties of the cell. They consist primarily of cellulose, variously modified by certain allied substances (lignin in wood, suberin in cork). These are all insoluble in ordinary solvents and in the alimentary canal of man. They are therefore so much useless "ballast" in the administration of the drugs. The processes of pharmacy consist largely in isolating the active constituents from this useless material.

Pharmacognostic Importance of Microscopic Structure.—The appearance, size and arrangement of the cells and their inclosures (starch grains, etc.) is often the most important aid in identifying a drug, particularly when in the form of powder. The pharmacopeias therefore include microscopic descriptions, whenever these are important.

Elementary and Proximate Constituents.—The elementary or ultimate,constituents of plants, as of animals, are mainly C, H, O, and N. The chemical compounds formed from these are called the proximate principles or constituents of the plant. These belong to the chemical groups of proteins, fats, carbohydrates, tannins, resins, alkaloids, glucosids, acids, terpenes, etc. Plants also contain inorganic salts. Cellulose.—This is found in the cell walls. It exists in almost pure form in cotton. It is chemically an isomer of starch, having the elementary formula (C6H10O5)n. It is insoluble in all the ordinary solvents, and is not affected by boiling water. It dissolves without change in Schweitzer's reagent (ammoniated solution of copper sulphate). In older cells it is often modified by the introduction of allied molecules: wood (lignin) or cork (suberin). Cork is very resistant to reagents and impermeable to water, and hence protects the plant against evaporation and chemic injury. The cellulose may also undergo a retrograde metamorphosis into gum or pectin. Starch (C6H10O5)n.—This is produced as one of the first stages in the assimilation of CO2. It occurs in the form of granules, usually showing a laminated structure around a center (hilus). The character of this lamination, as well as the average shape and size of the granules, are important in distinguishing between different plants.

Starch can be easily recognized by the blue color which it gives with iodin. It is insoluble in all the ordinary solvents, but with boiling water swells and forms a peculiar colloidal solution (paste).

Gums.—These are colloidal carbohydrates, swelling or dissolving in water to viscous adhesive fluids (mucilages or pastes). They are precipitated by alcohol. They are formed in the plant by the transformation of cellulose and cell contents, especially as the result of pathologic processes. Pectins are closely related substances, occurring in fruits, and