TCD consist of natural substances, such as plants, whole or parts of animals, and minerals. As stated above, drugs of plant origin are the main part of TCD. Their species, habitat, collection and storage are important factors determining their quality and therapeutic effectiveness.
3.1 Varieties of TCD
Some TCD occur in a number of varieties. This is due to the similarity of appearance of different plants grown in different places. Ancient doctors in different places used local types. But, in fact, the varieties sometimes are not of the same potency, due to the difference in the content of active principles. Some of them even have no effect. Hence, in clinical use as well as in experimental study, identification of the authentic family and species of the drug is of great importance.
3.2 Habitat of TCD
Most of the TCD are of plant origin. The quality of the soil in different places may not be the same, and so the content of active principles may not be the same in drugs of same family and species grown in different places. The quality of water and the local climate (hours of sunshine, rainfall, etc.) are also influencing factors. Thus, in ancient times there were so-called “genuine” drugs, which meant drugs of the right species, grown at the place where the drug is of the highest potency and the first one of the kind used. Nowadays, many TCD, both of plant and animal origin, are artificially grown in order to meet the increasing needs. Their quality has been studied and controlled.
3.3 Collection of TCD
The quality of drugs is closely related to the time, season and method of collection. The amount and quality of active ingredients in drugs of plant or animal origin vary greatly in the course of growth. The TCM classic called Supplement to the Essential Prescriptions Worth a Thousand Pieces of Gold states that if a drug is not collected at the right time it may be as worthless as a piece of rotten wood.
In general, a drug consisting of leaves or an entire herbaceous plant should be collected when its flowers are in full boom. For example, the total alkaloid content in Herba Leonuri when its flowers are in full bloom is 1.26 percent, while it is 0.39 percent when its fruits are ripe. Most drugs from flowers should be collected when the flowers are blooming. But some of them should be collected when the flowers are still in bud. For example, the content of rutin in the flowers of the Chinese scholartree is 13 percent, while in the buds it is 23.5 percent. Drugs from fruits are usually collected when the fruits are ripe. But some such drugs should be collected when the fruits are immature, for example, immature bitter orange and Tibet Fructus Canarii. Drugs from roots or rhizomes should be collected in late autumn or spring. Drugs from bark should be collected in spring or early summer.
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