Meaning of Pharmacognosy
Pharmacognosy, known initially as materia medica, may be defined as the study of crude drugs obtained from plants, animals, and mineral kingdom and their constituents. There is historical misinformation about who created the term pharmacognosy. According to some sources, it was C. A. Seydler, a medical student at Halle, Germany, in 1815; he wrote his doctoral thesis titled Analectica Pharmacognostica. However, recent historical research has found an earlier usage of this term. The physician J. A. Schmidt (Vienna) used that one in his Lehrbuch der materia medica in 1811, to describe the study of medicinal plants and their properties. The word pharmacognosy is derived from two Latin words pharmakon, ‘a drug,’ and gignoso, ‘to acquire knowledge of ’. It means ‘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 come from animal and mineral kingdoms. Drugs obtained from plants consist of entire plants, whereas senna leaves and pods, nux vomica seeds, ginger rhizome, and cinchona bark are parts of plants. Though in a few cases, as in lemon and orange peels and colchicum corm, drugs are used in fresh conditions, and most of the drugs are dried after collections. Crude drugs may also be obtained by simple physical processes like drying or extraction with water. Therefore, aloe is the dried juice of leaves of Aloe species, opium is the dried latex from poppy capsules and black catechu is the dried aqueous extract from the wood of Acacia catechu. Plant exudates such as gums, resins and balsams, volatile oils, and fixed oils are also considered crude drugs.
Further drugs used by physicians and surgeons or pharmacists, directly or indirectly, like cotton, silk, jute, and nylon in surgical dressing or kaolin; diatomite used in filtration of turbid liquid or gums; wax, gelatin, agar used as pharmaceutical auxiliaries of flavoring or sweetening agents or drugs used as vehicles or insecticides are used in pharmacognosy.
Drugs obtained from animals are entire animals, as cantharides; glandular products, like thyroid organs, or extracts like liver extracts. Similarly, fish liver oils, musk, beeswax, certain hormones, enzymes, and antitoxins are products obtained from animal sources.
Drugs are organized or unorganized. Organized drugs are direct parts of plants and consist of cellular tissues. Unorganized drugs, even though prepared from plants are not the direct parts of plants and are prepared by some intermediary physical processes, such as incision, drying, or extraction with water, and do not contain cellular tissue. Thus aloe, opium, catechu, gums, resins, and other plant exudates are unorganized drugs.
Drugs from mineral sources are kaolin, chalk, diatomite, and other bhasmas of Ayurveda.
Origin of Pharmacognosy
Views on the beginning of life on planet Earth have forever remained controversial and an unending subject of debate. Nevertheless, we can say with certainty that the vegetable kingdom was already there when man made his appearance on Earth. As the man began to acquire closure acquaintance with his environment, he began to know more about plants, as these were the only curative agents he had. As he progressed and evolved, he was not only able to sort on as to which plant served for eating and which did not, but he went beyond and began to associate curative characteristics with certain plants, classifying them as painkillers, febrifuge, antiphlogistics, soporific and so on. This must-have involved no doubt, a good deal of trial and error, and possibly some deaths in the beginning also, but as it happened antidotes against poisons were also discovered. As we shall see later, drug substitutes were also forthcoming. All these states of affairs indicate that the origin of pharmacognosy, i.e. the study of natural curative agents points towards the accent of human beings on mother earth, and its historical account makes it clear that pharmacognosy in its totality is not the work of just one or two continental areas but the overall outcome of the steadfast work of many of the bygone civilizations like the Chinese, Egyptian, Indian, Persian, Babylonian, Assyrian and many more. Many of today’s wonderful modern drugs find their roots in the medicines developed by the tribal traditions in various parts of the world.
History of Pharmacognosy
In the early period, the primitive man went in search of food and ate at random, plants or their parts like tubers, fruits, leaves, etc. As no harmful effects were observed he considered them as edible materials and used them as food. If he observed other effects by their eating they were considered inedible, and according to the actions he used them in treating symptoms or diseases. If it caused diarrhea it was used as purgative, if vomiting it was used as memtic and if it was found poisonous and death was caused, he used it as an arrow poison. The knowledge was empirical and was obtained by trial and error. He used drugs as such or as their infusions and decoctions. The results were passed on from one generation to the other, and new knowledge was added in the same way.
Chinese pharmacy, according to legend, stems from Shen Nung (about 2700 B.C.), an emperor who sought out and investigated the medicinal value of several hundred herbs. He reputed to have tested many of them on himself and to have written the first Pen T-Sao, or Native Herbal, recording 365 drugs. These were subdivided as follows: 120 emperor herbs of high, food-grade quality which is non-toxic and can be taken in large quantities to maintain health over a long period, 120 minister herbs, some mildly toxic and some not, having stronger therapeutic action to heal diseases and finally 125 servant herbs that having specific action to treat disease and eliminate stagnation. Most of those in the last group, being toxic, are not intended to be used daily over a prolonged period of weeks and months. Shen Nung conceivably examined many herbs, barks and roots brought in from the fields, swamps, and woods that are still recognized in pharmacy (podophyllum, rhubarb, ginseng, stramonium, cinnamon bark, and ephedra).
Inscriptions on oracle bones from the Shang Dynasty (1766–1122 B.C.), discovered in Honan Province, have provided a record of illness, medicines, and medical treatment. Furthermore, several medical treatises on silk banners and bamboo slips were excavated from tomb number three at Ma-Huang-Tui in Changsha, Hunan Province. These were copied from books sometime between the Chin and Han periods (300 B.C.–A.D. 3) and constitute the earliest medical treatises existing in China.
The most important clinical manual of traditional Chinese medicine is the Shang Hang Lun (Treatise on the Treatment of Acute Diseases Caused by Cold) written by Chang Chung-Ching (142–220). The fame and reputation of the Shang Han Lun as well as its companion book, Chin Kuei Yao Lueh (Prescriptions from the Golden Chamber), is the historical origin of the most important classical herbal formulas that have become the basis of Chinese and Japanese-Chinese herbalism (called ‘Kampo’).
With the interest in alchemy came the development of pharmaceutical science and the creation of several books including Tao Hong Jing’s (456–536) compilation of the Pen T’sao Jing Ji Zhu (Commentaries on the Herbal Classic) based on the Shen Nong Pen T’sao Jing, in 492. In that book, 730 herbs were described and classified into six categories: (1) stone (minerals), (2) grasses and trees, (3) insects and animals, (4) fruits and vegetables, (5) grains, and (6) named but unused. During the Sui dynasty (589–618) the study of herbal medicine blossomed with the creation of specialized books on plants and herbal medicine. Some of these set forth the method for the gathering of herbs in the wild as well as their cultivation. Over 20 herbals were chronicled in the Sui Shu JingJi Zhi (Bibliography of the History of Sui). These include the books Zhong Zhi Yue Fa (How to Cultivate Herbs) and the Ru Lin Cat Yue Fa (How to Collect Herbs in the Forest).
From the Sung Dynasty (960–1276) the establishment of the pharmaceutical system has been a standard practice throughout the country. Before the ingredients of Chinese medicine can be used to produce pharmaceuticals, they must undergo a preparation process, e.g. baking, simmering, or roasting. The preparation differs according to the needs for the treatment of the disease. Preparation methods, production methods, and technology have constantly been improved over time.
In 1552, during the later Ming Dynasty, Li Shi Zhen (1518–1593) began work on the monumental Pen T’sao Kan Mu (Herbal with Commentary). After 27 years and three revisions, the Pen T’sao Kan Mu was completed in 1578. The book lists 1892 drugs, 376 described for the first time with 1160 drawings. It also lists more than 11,000 prescriptions.
The most complete medical documents existing are the Ebers Papyrus (1550 B.C.), a collection of 800 prescriptions, mentioning 700 drugs, and the Edwin Smith Papyrus (1600 B.C.), which contains surgical instructions and formulas for cosmetics. The Kahun Medical Papyrus is the oldest-it comes from 1900 B.C. and deals with the health of women, including birthing instructions.
However, it is believed that the Smith Papyrus was copied by a scribe from an older document that may have dated back as far as 3000 B.C. Commonly used herbs included: senna, honey, thyme, juniper, cumin, (all for digestion); pomegranate root, henbane (for worms) as well as flax, oak gall, pine tar, manna, bayberry, Ammi, alkanet, aloe, caraway, cedar, coriander, cyperus, elderberry, fennel, garlic, wild lettuce, nasturtium, onion, peppermint, papyrus, poppy-plant, saffron, watermelon, wheat, and zizyphus-lotus. Myrrh, turpentine, and acacia gum were also used.
In India knowledge of medicinal plants is very old, and the medicinal properties of plants are described in Rigveda and in Atharvaveda (3500–1500 B.C.) from which Ayurveda has developed. The basic medicinal texts in this world region. The Ayurvedic writings can be divided into three main ones (Charaka Samhita, Susruta Samhita, Astanga Hrdayam Samhita) and three minor ones (Sarngadhara Samhita, Bhava Prakasa Samhita, Madhava Nidanam Samhita). Ayurveda is the term for the traditional medicine of ancient India. Ayur means life and Veda means the study of which is the origin of the term. The oldest writing Charaka Samhita is believed to date back six to seven centuries before Christ. It is assumed to be the most important ancient authoritative writing on Ayurveda. The Susruta Samhita is thought to have arisen about the same time as the Charaka Samhita, but slightly after it, Astanga Hrdayam and the Astanga Sangraha have been dated about the same time and are thought to date after the Charaka and Susruta Samhitas. Most of the mentioned medicines originate from plants and animals, e.g. Ricinus, Pepper, Lilly, Valerian, etc.
Ancient Greece and Rome
Greek scientists contributed much to the knowledge of natural history. Hippocrates (460–370 B.C.) is referred to as the father of medicine and is remembered for his famous oath which is even now administered to doctors. Aristotle (384–322 B.C.), a student of Plato was a philosopher and is known for his writing on the animal kingdom which is considered authoritative even in the twentieth century. Theophrastus (370–287 B.C.), a student of Aristotle, wrote about the plant kingdom. Dioscorides, a physician who lived in the first century A.D., described medicinal plants, some of which like belladonna, ergot, opium, colchicum are used even today. Pliny wrote 37 volumes of natural history and Galen (131–A.D. 200) devised methods of preparations of plant and animal drugs, known as ‘galenicals’ in his honor.
Pharmacy separated from medicine and materia medica, the science of material medicines, describing the collection, preparation and compounding, emerged.
Even up to the beginning of the twentieth century, pharmacognosy was more of a descriptive subject akin mainly to botanical science, and it consisted of identification of drugs both in entire and powdered conditions and was concerned with their history, commerce, collection, preparation, and storage.
The development of modern pharmacognosy took place later during the period 1934 – 1960 by simultaneous application of disciplines like organic chemistry, biochemistry, biosynthesis, pharmacology, and modern methods and techniques of analytic chemistry, including paper, thin layer, and gas chromatography and spectrophotometry.
The substances from the plants were isolated, their structures elucidated and pharmacological active constituents studied. The development was mainly due to the following four events:
- Isolation of penicillin in 1928 by William Fleming and large-scale production in 1941 by Florey and Chain.
- Isolation of resperpine from rauwolfia roots and confirming its hypotensive and tranquilizing properties.
- Isolation of vinca alkaloids, especially vincristine and vinblasting. Vincristine was found useful in the treatment of leukemia. These alkaloids also have anti-cancer properties.
- Steroid hormones like progesterone were isolated by partial synthesis from diosgenin and other steroid saponins by Marker’s method. Cortisone and hydrocortisone are obtained from progesterone by chemical and microbial reactions.
This period can also be termed antibiotic age, as besides penicillin, active antibiotics like streptomycin, chloramphenicol, tetracycline, and several hundred antibiotics have been isolated and studied extensively.
Some of the important aspects of the natural products that led to the modern development of drugs and pharmaceuticals are as follows:
Isolation of phytochemicals
Strong acting substances such as glycosides of digitalis and scilla, alkaloids of hyoscyamus and belladonna, ergot, rauwolfia, morphine, and other alkaloids of opium were isolated and their clinical uses studied.
Tubocurarine and toxiferine from curare have muscle relaxant properties because of quaternary ammonium groups. The hypotensive and tranquilizing actions of reserpine are attributed to the trimethoxy benzoic acid moiety which is considered essential. Mescaline and psilocybin have psychoactive properties. The presence of a lactone ring is essential for the action of cardiac glycosides. Likewise, anthraquinone glycosides cannot have their action without satisfying the positions at C3, C1, C8, C9, and C10.
Drugs obtained by partial synthesis of natural products
The oxytocic activity of methyl ergometrine is more than that of ergometrine. In ergotamine, by 9:10 hydrogenation, oxytocic activity is suppressed, and spasmolytic activity increases. We have already referred to the preparation of steroid hormones from diosgenin by acetolysis and oxidation and further preparation of cortisone by microbial reactions.
Steroid hormones and their semisynthetic analogs represent a multimillion-dollar industry in the United States.
Natural products as models for the synthesis of new drugs
Morphine is the model of a large group of potent analgesics, cocaine for local anesthetics, atropine for certain spasmolytics, dicoumarol for anticoagulants, and salicin for salicylic acid derivatives. Without model substances from plants, a large number of synthetics would have been missed.
Drugs of direct therapeutic uses
Among the natural constituents, which even now cannot be replaced, are important groups of antibiotics, steroids, ergot alkaloids, and certain antitumor substances. Further, drugs as digitoxin, strophanthus glycosides, morphine, atropine, and several others are known for long and have survived their later day synthetic analogs.
Biosynthetic pathways are of primary and secondary metabolites. Some of the important pathways are Calvin’s cycle of photosynthesis, the shikimic acid pathway of aromatic compounds, acetate hypothesis for anthracene glycosides, and isoprenoid hypothesis for terpenes and steroids via acetate-mevalonic acid-isopentyl pyrophosphate and squalene.
Progress from 1960 onwards
During this period only a few active constituents mainly antibiotics, hormones, and antitumor drugs were isolated or new possibilities for their production were found. From 6-amino penicillanic acid, which has very little antibiotic action of its own, important broad-spectrum semisynthetic penicillins like ampicillin and amoxicillin were developed.
From ergocryptine, an alkaloid of ergot, bromocryptine has been synthesized. Bromocryptine is a prolactin inhibitor and also has activity in Parkinson’s disease and cancer. By applications of several disciplines, pharmacognosy from a descriptive subject has again developed into an integral and important discipline of pharmaceutical sciences.
Natural products, besides being used as drugs and therapeutic aids, are used in several other industries like beverages, condiments, spices, confectioneries, and technology products.
Coffee beans and tea leaves besides being the source of caffeine are used as popular beverages. Ginger and wintergreen oil are used less pharmaceutically but are more used in the preparation of soft drinks. Mustard seed and clove are used in spice and the condiment industry. Cinnamon oil and peppermint oil besides being used as carminatives are used as flavoring agents in candies and chewing gum. Colophony resin, turpentine oil, linseed oil, acacia, pectin, and numerous other natural products are used widely in other industries and are called technical products.
Some of the natural products obtained from plants and animals are used as pharmaceutical aids. Thus gums like acacia and tragacanth are used as binding, suspending, and emulsifying agents. Guar gum is used as a thickening agent and as a binder and as a disintegrating agent in the manufacturing of tablets. Sterculia and tragacanth because of their swelling property are used as bulk laxative drugs. Mucilage-containing drugs like ishabgul and linseed are used as demulcents or as soothing agents and as bulk laxatives. Starch is used as a disintegrating agent in the manufacture of tablets and because of its demulcent and absorbent properties, it’s used in dusting powders. Sodium alginate is used as an establishing, thickening, emulsifying deflocculating, gelling and filming agent. Carbohydrate-containing drugs like glucose, sucrose, and honey are used as sweetening agents and as a laxative by osmosis.
Agar, in addition to being used as a laxative by osmosis, is also used as an emulsifying agent and in culture media in microbiology. Saponins and sponin-containing drugs are used as detergents, emulsifying and frothing agents, and as fire extinguishers. Tincture quillaia is used in the preparation of coal tar emulsions. Saponins are toxic and their internal use requires great care, and in some countries, their internal use as frothing agents is restricted. Glycyrrhiza is used as a sweetening agent for masking the taste of bitter and salty preparations.
Fixed oils and fats are used as emollients and as ointment bases and vehicles for other drugs. Volatile oils are used as flavoring agents.
Gelatin is used in the coating of pills and tablets and preparation of suppositories, as culture media in microbiology, and preparation of artificial blood plasma. Animal fats like lard and suet are used as ointment bases. Beeswax is used as an ointment base and thickening agent in ointments. Wool fat and wool alcohols are used as absorbable ointment bases.
Thus, from the above description, it can be seen that many of the natural products have applications as pharmaceutical aids.
Discovery of new medicines from plants-nutraceutical use versus drug development
Little work was carried out by the pharmaceutical industry during 1950-1980s; however, during the 1980–1990s, massive growth has occurred. This has resulted in new developments in the area of combinatorial chemistry, new advances in the analysis and assaying of plant materials, and a heightened awareness of the potential plant materials as drug leads by conservationists. New plant drug development programs are traditionally undertaken by either random screening or an ethnobotanical approach, a method based on the historical medicinal/food use of the plant. One reason why this area has been resurgent is that conservationists especially in the United States have argued that by finding new drug leads from the rainforest, the value of the rainforests to society is proven and that this would prevent these areas from being cut down for unsustainable timber use. However, tropical forests have produced only 47 major pharmaceutical drugs of worldwide importance. It is estimated that a lot more, say about 300 potential drugs of major importance may need to be discovered. These new drugs would be worth $147 billion. It is thought that 125,000 flowering plant species are of pharmacological relevance in tropical forests. It takes 50,000 to 100,000 screening tests to discover one profitable drug. Even in developed countries, there is a huge potential for the development of nutraceuticals and pharmaceuticals from herbal materials. For example, the UK herbal materia medica contains around 300 species, whereas the Chinese herbal materia medica contains around 7,000 species. One can imagine what lies in store in the flora-rich India!
Scope of Pharmacognosy
Crude drugs of natural origin that are obtained from plants, animals, and mineral sources and their active chemical constituents are the core subject matter of pharmacognosy. These are also used for the treatment of various diseases besides being used in cosmetic, textile and food industries. During the first half of the nineteenth-century apothecaries stocked the crude drugs for the preparation of herbal tea mixtures, all kinds of tinctures, extracts, and juices which in turn were employed in preparing medicinal drops, syrups, infusions, ointments, and liniments.
The second half of the nineteenth century brought with it several important discoveries in the newly developing fields of chemistry and witnessed the rapid progress of this science. Medicinal plants became one of its major objects of interest and in time, phytochemists succeeded in isolating the pure active constituents. These active constituents replaced the crude drugs, with the development of semisynthetic and synthetic medicine, they became predominant and gradually pushed the herbal drugs, which had formerly been used, into the background. It was a belief that the medicinal plants are of no importance and can be replaced by man-made synthetic drugs, which in today’s scenario is no longer tenable. The drug plants, which were rapidly falling into disuse a century ago, are regaining their rightful place in medicine. Today applied science of pharmacognosy has a far better knowledge of the active constituents and their prominent therapeutic activity on human beings. Researchers are exploiting not only the classical plants but also related species all over the world that may contain similar types of constituents. Just like terrestrial germplasm, investigators had also diverted their attention to marine flora and fauna, and wonderful marine natural products and their activities have been studied. Genetic engineering and tissue culture biotechnology have already been successful for the production of genetically engineered molecules and biotransformed natural products, respectively.
Lastly, crude drugs and their products are of economical importance and profitable commercial products. When these were collected from wild sources, the amount collected could only be small, and the price commanded was exorbitantly high. All this has now changed. Many of the industrially important species which produced equally large economic profits are cultivated for large-scale crop production. Drug plants, standardized extracts, and therapeutically active pure constituents have become a significant market commodity in international trade. In the light of these glorious facts, the scope of pharmacognosy seems to be enormous in the field of medicine, bulk drugs, food supplements, pharmaceutical necessities, pesticides, dyes, tissue culture biotechnology, engineering, and so on.
The scope for doctoral graduates in pharmacognosy is going to increase in the coming years. The pharmacognosist would serve in various aspects as follows:
Academics: Teaching in colleges, universities, museums, and botanical gardens.
Private industry: Pharmaceutical companies, consumer products testing laboratories and private commercial testing laboratories, the herbal product industries, the cosmetic and perfume industries, etc.
Government: Placement in federal agencies, such as the Drug Enforcement Agency, the Food and Drug Administration, the U.S. Department of Agriculture, Medicinal plant research laboratories, state agencies like forensic laboratories, environmental laboratories, etc.
Undoubtedly, the plant kingdom still holds a large number of species with a medicinal value that has yet to be discovered. Lots of plants were screened for their pharmacological values like, hypoglycaemic, hepatoprotective, hypotensive, anti-inflammatory, antifertility, etc. pharmacognosists with a multidisciplinary background can make valuable contributions in the field of phytomedicines.
Future of Pharmacognosy
Medicinal plants are of great value in the field of treatment and cure of disease. Over the years, scientific research has expanded our knowledge of the chemical effects and composition of the active constituents, which determine the medicinal properties of plants. It has now been a universally accepted fact that plant drugs and remedies are far safer than synthetic medicines for curing complex diseases like cancer and AIDS. An enormous number of alkaloids, glycosides, and antibiotics have been isolated, identified, and used as curative agents. The modern developments in the instrumental techniques of analysis and chromatographical methodologies have added numerous complex and rare natural products to the armory of phytomedicine. To mention a few, artemisinin as antimalarial, taxol as anticancer, forskolin as antihypertensive, rutin as vitamin P and capillary permeability factor, and piperine as bioavailability enhancer are the recent developments. Natural products have also been used as drug substitutes for the semisynthesis of many potent drugs. Ergotamine for dihydroergotamine in the treatment of migraine, podophyllotoxin for etoposide, a potent antineoplastic drug or solasodine, and diosgenin that serve for the synthetic steroidal hormones are the first-line examples of the recent days.
In the Western world, as people are becoming aware of the potency and side effects of synthetic drugs, there is an increasing interest in plant-based remedies with a basic approach towards nature. The future developments of pharmacognosy, as well as the herbal drug industry, would be largely dependent upon the reliable methodologies for identification of marker compounds of the extracts and also upon the standardization and quality control of these extracts. Mother earth has given vast resources of medicinal flora and fauna both terrestrial and marine, and it largely depends upon the forthcoming generations of pharmacognosists and phytochemists to explore the wonder drug molecules from this unexploited wealth.
Little more needs to be said about the present-day importance of medicinal plants, for it will be apparent from the foregoing that the plant themselves either in the form of crude drugs or even more important, for the medicinally active materials isolated from them, have been, are and always will be an important aid to the physician in the treatment of disease.
To describe drugs systematically is known as a pharmacognostic scheme, which includes the following headings:
This includes the biological names of plants or animals yielding the drug and the family to which it belongs. The botanical name includes genus and species. Often some abbreviations are written after the botanical names, of the biologist responsible for the classification, for example, Acacia arabica Willd. Here Willd indicates the botanist responsible for the classification of nomenclature. According to the biennial theory, the botanical name of any plant or animal is always written in italic form, and the first letter of a genus always appears in the capital later.
The biological source also includes the family and the part of the drug used. For example, the biological source of senna is, Senna consists of dried leaflets of Cassia Angustifolia Delite, belonging to the family Leguminosae.
It includes the areas of cultivation, collection, and route of transport of a drug.
Cultivation, Collection, and Preparation
These are important to mention as they are responsible for the quality of a drug.
In the case of organized drugs, the length, breadth, thickness, surface, color, odor, taste, shape, etc. are covered under the heading morphological characters, whereas organoleptic properties (color, odor, taste, and surface) should be mentioned, if the drug is unorganized.
This is one of the important aspects of pharmacognosy as it helps in establishing the correct identity of a drug. Under this heading, all the detailed microscopical characters of a drug are described.
The most important aspect which determines the intrinsic value of a drug to which it is used is generally described under this heading. It includes the chemical constituents present in the drug. These kinds of drugs are physiologically active.
It includes the pharmaceutical, pharmacological, and biological activity of drugs or the diseases in which it is effective.
The drug which is used during the non-availability of the original drug is known as a substituent. It has the same type of physiological active constituents; however, the percentage quantity of the drug available may be different.
With the knowledge of the diagnostic characters of drugs, adulterants can be detected. One should have critical knowledge of substances known to be potential adulterants. Most of the time the adulterants are completely devoid of physiologically active constituents, which leads to the deterioration of the quality. For example, mixing buffalo milk with goat milk is a substitution, whereas mixing of water in the milk is adulteration. In the first case, goat milk is a substitute and in the second case water is an adulterant.
The knowledge of chemical tests becomes more important in the case of unorganized drugs whose morphology is not well defined.
Make sure you also check our other amazing Article on : Pharmacognosy of Aloe