Collection of medicinal plants Drugs may be collected from wild or cultivated plants. It is known that the active constituents of medicinal plants are affected by many factors and may vary during the course of plant growth. Proper time of collection is very important to obtain a drug of a good quality.

Factors affecting collection 1.Time of the year: The plant may contain a substance in winter that is not present in summer, or its amount varies markedly e.g. Rhubarb contains no anthraquinone in winter, instead it contains anthranols, which in summer, are oxidized to anthraquinones. Colchicum corm is free from bitterness and is devoid of the alkaloid colchicine in autumn, hence is used in Austria as a food, instead of potatoes. Bitterness starts to appear in spring and early summer when it is used as a drug.

2- Time of the day: Some drugs, like Digitalis, contain different amounts of active constituents in different times of the day. Being highest in the afternoon.

3- Stage of maturity and age: The value and content of active constituents of many drugs depends on the stage of maturity and age. Conium fruits contain coniin when fruits are mature and unripe. Santonica flowers are rich in santonin, when unexpanded, when it starts to open, the santonin content decreases.

Drying of crude drugs Reasons for drying: 1.To help in their preservation. 2.To fix their constituents, by preventing reactions that may occur in presence of water. 3.To prevent the growth of micro-organisms such as bacteria and fungi. 4.To facilitate their grinding. 5.To reduce their size and weight. 6.Insufficient drying favors spoilage by micro- organisms and makes it possible for enzymatic destruction.

Methods of drying Drying is carried out either by natural or artificial methods. 1- Natural drying: this is accomplished by natural air in sun or shade. 2- Artificial drying: this is a rapid method done at well-controlled temperature and is accomplished by: direct fire. Use of heated stones. Use of stoves.

Disadv. of natural drying: Drying should be done carefully to prevent damage or burning. Excessive heat cause gelatinization of starch, as well as, a smoky odour. Drying chambers: this method provides a controlled process. Drying chambers consist of closed space with several movable screen trays, arranged so as to allow the circulation of heated air. Its temperature and ventilation can be regulated to suit drying of different organs.

Lypholyzation (Freeze drying) Chemical drying using desiccators An absolutely dried drug is that completely freed from water, when exposed to air it absorbs 8-10% of moisture and is called air-dry drug.

Several changes may occur on drying: 1.Size and weight: markedly decreases due to loss of 80-90% of water. 2.Shape and appearance: some drugs shrivel on drying, others have their surface wrinkled or reticulated. 3.The method of drying also affects the appearance of some unorganized drugs. aloes, when rapidly heated and cooled, produces homogenous glassy masses but when slowly heated and cooled produces heterogeneous opaque masses.

4- Texture: drugs on drying become harder ( roots), brittle (leaves) while those containing starch become horny. 5- Colour: generally on drying, drugs become darker in colour and in certain cases a total change of colour occurs, e.g. poppy, when fresh is scarlet-red, on drying becomes dull-violet. Tea leaves change from green to brown almost black. Flowers may lose their colour especially when red or blue due to destruction of anthocyanin pigment responsible for the colour. 6- Odour: Hyoscyamus and Digitalis lose their bad odour on drying. Orris acquire a pleasant odour on drying.

7- Taste: this may be altered. Fresh Gentian is very bitter becoming pleasant on drying. 8- Constituents: some drugs containing sensitive constituents as cardiac glycosides may undergo certain degrees of hydrolysis during drying. Fresh Vanilla pods contain gluco-vanillin and gluco-vanillic alcohol. On drying, hydrolysis of both glycosides and oxidation to vanillin take place. Some changes are favorable and hence conditions should be made suitable to encourage such changes. On the other hand certain changes are undesirable and conditions should be controlled to guard against their occurrence.

Preservation and protection of crude drugs Storage represents the last stage of preparing crude drugs. drugs usually deteriorate along the time of storage, except in few cases e.g. Cascara and Frangula should not be used except after certain period of storage. Certain drugs as Nux vomica are hardly affected by storage. Generally, changes that take place during storage of crude drugs are objectionable, e.g. drugs containing volatile oils gradually lose their aroma. Improper methods of storing and inadequate protection during storage can cause a pronounced deterioration. There are two principal reasons for deterioration: Physiochemical: moisture, heat, air and light. Biological: fungi, bacteria, insects and rodents.

Physicochemical factors 1.Moisture: moisture sometimes affects drugs adversely through activating the enzymes (as in cardiac glycosides). 2.Heat: rise of temperature up to 45 activates the enzymes causing decomposition of active constituents. Volatile oil containing drugs are also affected by higher temperatures, their content decreases. 3.Air: oxygen of air oxidizes certain constituents of crude drugs, e.g. linseed and lemon oil, it causes rancidity of fixed oils and resinification of volatile oils. 4.Light: it affects drugs, especially those having marked colours.e.g. yellow colour of Rhubarb changes to reddish tint, white coloured corollas turn brown.

Biological factors 1.Bacteria: cotton fibres are rendered brittle by bacterial attack which makes the cotton wool objectionable and dusty. 2.Moulds: the mycelium of delicate hyphae produces an unpleasant mass of clinging particles in powdered drugs. 3.Insects: they seem to attack all drugs but have preferences to certain drugs as ginger, belladonna, kola, liquorice,..... Insects which infest vegetable drugs include beetles, mites and moths. They render drugs porous and powdery.

Methods for controlling insects 1.Heat treatment: it is the simplest method and is done by exposing the drug to a temperature of it is effective especially for insect eggs which are not affected by insecticides. 2.Fumigation: this is done by volatile insecticidal agents in closed areas e.g. CCL 4, CS 2, CN. Most fumigants do not kill eggs of insects. It is advisable to repeat fumigation at intervals to obtain better results.

3. Liming: liming of certain drugs as ginger, nutmeg to protect against insect attack provides only partial protection. 4. Low temperature storage: this method is preferred to fumigants and liming. Adult insects, pupae, larvae and eggs are sometimes killed by very low temperatures. 5. Exposure to alternate periods of low and high temperatures: frequently is more effective for killing insects than a prolonged period of low temperature exposure.

Rodents: they cause much spoilage of crude drugs during storage, especially if wrapped in paper, cloth or put in cardboard or wooden containers. The presence of rodent's filth, excreta, hairs causes rejection of the drug.