Natural drugs obtained from plants and animals are called drugs of biological origin and are produced in the living cells of plants or animals.
Natural drugs obtained from plants and animals are called drugs of biological origin and are produced in the living cells of plants or animals. Pharmacognosy is the study of crude drugs obtained from plants, animals and mineral kingdom. Even though the science of pharmacognosy is practised since a very early period, the term pharmacognosy was first used by Seydler, a German scientist, in 1815 in his book Analecta Pharmacognostica. It is derived from two Latin words pharmaka (a drug) and gignosco (to acquire a knowledge of). It means a knowledge or science of drugs. Crude drugs are plants or animals or their parts which after collection are subjected only to drying or making them into transverse or longitudinal slices or peeling them in some cases. Most of the crude drugs used in medicine are obtained from plants and only a small number comes from animal and mineral kingdom. Drugs obtained from plants consist of entire plants or their parts. Ergot, ephedra and datura are entire plants while senna leaves and pods, nux vomica seeds, ginger rhizomes and cinchona bark are parts of the plants. Though in few cases as in lemon and orange peels and in colchicum corm drugs are used in fresh condition, most of the drugs are dried after collection. Crude drugs may also be obtained by simple physical processes like drying or extraction with water. Thus the aloe is dried juice of leaves of aloe species, opium is the dried latex from poppy capsules and black catechu is the dried aquous extract from the wood of Acacia catechu. Further drugs used by doctors or pharmacists, directly or indirectly, like cotton, silk, jute, nylon in surgical dressings or kaolin, diatomite used in filtration of turbid liquids or gums, wax, gelatin, agar used as pharmaceutical auxiliaries or flavouring or sweetening agents or drugs used as vehicles or insecticides are treated in pharmacognosy. Drugs obtained from animals are either glandular products, like thyroid organ or extracts like liver extract. Simlarly, fish liver oils, musk, bees’ wax, certain hormones, enzymes and antitoxins are products obtained from animal sources. Drugs from mineral kingdom are kaolin, chalk, diatomite, the well- known Makardhwaj and other bhasmas of Ayurveda. A systematic and complete study of the drugs is done in pharmacognosy. In the systematic study of crude drugs (a). origin, common names, biological source and family; (b). geographical source; (c) history; (d). cultivation, collection, preparation for market and storage; (e) macroscopical, sensory and microscopical characters; (f). chemical constituents; (g). uses; (h). substitutes and adulterants and (i). evaluation are described. Each drug is always obtained from the same plant or animal. The Latin name of the plant or animal is called its botanical or zoological source. The family to which this plant or animal belongs is also mentioned, e.g. Vasaka leaves are obtained from Adhatoda vasica plant; family Acanthaceae. Vasaka leaves are included in the Indian pharmacopoeia and are called official leaves. Their botanical source is called official source. Geographical source or habitat gives us information about the country or place where the drug is produced. Ginger is produced in Jamaica and nux vomica and ispaghula in India. In some cases the original native place of a drug is not the same as the present geographical source, e.g. cinchona is a native of South America and is at present cultivated in Indonesia, India and Congo. History of the drugs gives us useful information about how the drug was known, where it was growing originally and how it was introduced into the modern medicine. History of some drugs like cinchona bark, coca leaves, rauwolfia root and opium is very interesting. Politics play its part in the drugs also. Thus there is restriction on the import of buchu leaves growing in South Africa because of our political relations with that country. One of the requirements of the drugs is that they should possess maximum activity and thus should contain maximum percentage of active chemical constituents. For this reason many of the drugs like digitalis leaves, belladonna herb and roots, Ceylon cinnamon bark, linseed, fennel and other umbelliferous fruits are obtained from cultivated plants only. In cultivation attention is paid to the selection of proper strains of seeds, type of soil, optimum climatic factors like light, temperature, elevation, rainfall, etc. so that strong and sturdy plants rich in active chemical constituents would grow. The crude drugs obtained in this way are usually more active. Drugs are collected during definite season, time of the day and in special condition at a definite stage of development. Thus ephedra, wild cherry bark, most of the subterranean drugs consisting of roots and rhizomes are collected in autumn. Leaf drugs are collected during the flowering season. Solanaceous herbs like hyoscyamus, belladonna etc. are collected in the morning and during the dry weather. Clove is collected in bud condition, santonica when flower heads are closed, chamamile flowers when fully expanded and coriander fruits when completely ripe. However, some of the drugs, mostly because of economic considerations, are obtained from wild plants. Thus gentian root in Europe, nux vomica seeds in India and strophanthus seeds in Africa are obtained from wild plants. Crude drugs consist of definite parts of the plants, e.g. leaf, flower, fruit seed, wood bark, root etc. Morphological or macroscopical description of these parts is undertaken with naked eye or with magnifying lens. In this description general condition of the drug, size, shape, outer surface, inner surface, fracture etc. are described. Thus each part of the plant is described to a definite system characteristic of each group. Drugs can be identified as above only if they are in entire condition. Sensory or organoleptic characters describe colour, odour, taste, consistency etc. By the sensory characters often useful information is obtained. If leaf drugs are not thoroughly dried they are tough or flexible but if over-dried they become brittle. If leaves, flowers, and some herbs like lobelia are dried directly in the sunlight they become pale, bleached and yellow but retain green colour if dried in shade. Different species of mentha can be determined by an experienced worker by smell only. In ergot rancid and ammoniacal odour indicates inferior drug. Taste tells us about bitter drugs like nux vomica and pungent drugs like ginger and capsicum. If the drugs are in broken or even in powdered condition their microscopic characters are studied by use of microscope. In case of leaves, surface preparation and transverse section, preferably through mid-rib, are made and nature of epidermis, trichomes, stomata, arrangement of tissues like palisade cells, vascular bundles and nature of cell-contents are studied Similarly in case of barks, roots, rhizomes and wood, transverse and longitudinal sections are made and from characteristic arrangement of tissues of each drug and from diagnostic elements like stone cells, fibres, vessels etc. the drugs are identified. The diagnostic elements persist even when the drugs are in fine powdered condition and help in identification of the drugs. The sections or the powdered drug samples are cleared by clearing agents, mostly by chloral hydrate solution, before mounting on the slide. The basic chemical nature of cell-wall of almost all the plants is cellulosic. However, lignin, suberin, cutin or mucilage are deposited to the cellulose. Cellulose gives blue colour with chlor-zine iodine solution or with cuoxam (copper-oxide-ammonia) reagent. Lignin is present in the middle lamella and secondary cell-walls of many vessels, fibres and scleroids and gives red colour with phloroglucinol and concentrated hydrochloric acid. Suberin is present in cork and endodermis cells while cutin in the cuticle of leaf. Both are fatty in nature and when heated with Sudan red III give red colour. Mucilage gives red colour with ruthenium red. The chemical constituents present in the drugs can be identified by chemical or micro-chemical tests. Cascara bark and rhubarb rhizome give with 5% potassium-hydroxide red colour because of anthraquinone derivatives. Strychnine present in nux vomica gives purplish-red colour with ammonium vanadate and concentrated sulphuric acid. Paper chromatography and thin layer chromatography are utilized in identification of drugs, their adulterants and their chemical constituents. Methods have been developed for quantitative estimation of the chemical constituents from paper and thin layer chromatography. Drugs contain chemical constituents in different proportions which give us information about active and other constituents. Thus quinine is an alkaloid present in cinchona bark; eugenol is a constituent of clove oil; wild cherry bark contains cyanogenetic glycosides; jalap and podophyllum contain resins and mucilage is the chemical constituent of ispaghula and linseed. The study of pharmacognosy also includes the use of drugs and the pharmacological action of their chemical constituents. Thus cinchona bark is used in malaria, rauwolfia root in high blood-pressure and in insanity, digitalis in cardiac diseases etc. Some drugs or their products have pharmaceutical applications, e.g. starch as distintegrating agent in tablets, gum as binding and suspending agent, agar as emulsifier and diatomite for filtration. Sometimes crude drugs are adulterated. An adulterant is the drug resembling the original or authentic drug but usually quite different or inferior, less effective, containing less percentage of active constituents and sometimes containing more extraneous matter than permitted.. Nature of adulteration can be determined by the study of pharmacognosy. Evaluation of the drugs means determining their identity, purity and quality or activity. According to Claus evaluation can be expressed through (a). orgamoleptic and morphological evaluation, (b). microscopical evaluation, (c). biological evaluation, (d) physical evaluation and (e) chemical evaluation. In organoleptic evaluation macroscopical and sensory characters are mentioned. In microscopical evaluation, microscopic characters of drugs are described. In biological, physical and chemical evaluation quality or activity of the drug is determined. In the study of pharmacognosy drugs are arranged according to the following systems of classification: (1) Morphological classification, (2) Biological (Taxonomical) classification, (3) Chemical classification, and (4) Pharmacological classification.