Preparing Medicinal Plants

Successful treatment with medicinal plants depends largely on their preparation for use. In popular medicine they are most often administered in the form of tisanes (teas), powders, or as pulps (gruels obtained by bruising the fresh tissues).

Powders must always be sufficiently fine to enable the digestive juices to extract the active principles. Administration in powder form allows the body to absorb these principles progressively and totally. It would be correct to regard this as the best method of usage. In general the requisite amount of powdered drug is suspended in a little water and then swallowed.

Vegetable pulps are most often applied to wounds. It is necessary to wash the plant or part of plant well, to place it on a clean surface and then bruise it with a blunt knife. The procedure is liable to introduce living micro-organisms into the wound.

Medicinal plants are most often administered in the form of tisanes (teas), which are prepared by either infusion or decoction.

Infusion consists of pouring boiling water on a suitable amount of drug and allowing to stand for 10-15 minutes; alternatively the drug and cold water are placed in a covered vessel, which is heated to boiling point, immediately removed from the source of heat and allowed to stand for 10-15 minutes; the second method is preferable.

Decoction consists of placing the drug in cold water, raising it to the boil, continuing the boiling for 10-15 minutes, then allowing to stand for a quarter of an hour. Many active constituents are altered by this process of decoction.

The fineness of the powder is of great importance; in most cases the active principles are enclosed within the vegetable cells from which they must be extracted by dissolution (infusion or decoction). Thus it is necessary to break barks, roots and woods or thick leaves such as bearberry into very small fragments before making tisanes from them. If this is not done, there is a danger that only a small part of the active constituents will pass into the tisane.

The choice between infusion and decoction depends mainly on the chemical properties of the active constituents present in the drug. In general terms drugs containing volatile oils are always treated by infusion never by decoction; this is generally the same for glycoside-containing drugs, but if the glycosides are only weakly soluble, the drug may be boiled for a short time (2-5 minutes).

Mucilaginous drugs are infused in order to avoid destroying the active principles, but drugs very rich in mucilage (e.g. seeds of linseed and quince) should be allowed to macerate for 10-30 minutes in cold water after which both the aqueous macerate and the drug itself are swallowed. But drugs containing tannins are, as a rule, allowed to boil for some minutes.

Where mixtures of drugs with different sensitivities to heat are to be used, it is best to use the method of preparation suitable to the most labile drug, reducing all woody tissues to small fragments in order to ensure good extraction of the active principles.

The amount of drug to be used depends both on the patient to be treated and on the nature of the drug used. In the descriptions of the plants the quantities to be used have always been indicated, but these should be reduced for weak patients and for children by age. they can then be used throughout the year.

Methods of drying may themselves also greatly influence the content of active constituents. It is of prime importance to dry the plants as soon as possible after collection in order to avoid changes that may occur, especially in the active principles.

Drying poses a number of problems in our humid climate. In warm and dry times, almost all medicinal plants may be dried in the air without any special apparatus. But in wet seasons, the commercial grower of medicinal plants must have special equipment; for example he may use the driers employed for fruits and vegetables; in which
case the temperature must be carefully regulated: plants containing volatile oils must be dried between 20 and 40° C (68-104° F), while many others will withstand temperatures between 15 and 80° C (59-176°F), although in general, active principles are best conserved between 50 and 70°C (122°158° F).

It is often said that drying should be carried out in the shade. This is certainly true for drugs containing volatile oils which, when dried in the sun, lose up to 30% of these constituents. Other plants do not appear to suffer any loss of active constituents when dried in the sun and cases are known (belladonna, foxglove) in which the amount of active principles is increased by drying in the sun.

In this case it is necessary only to expose the plant tissues to the rays of the sun for just the necessary time to dry them, after which they must be placed in the shade in order to avoid changes in appearance and possibly also in their activity.

Whichever method is selected(in the shade, in sunlight, in a drying apparatus), it is important to spread the plants in thin layers without any overlaying of different parts. If this precaution is not taken, the drying is greatly slowed down and fermentation may occur with loss of active principles. To air-dry small quantities, well ventilated lofts are used. For larger quantities of drugs it is satisfactory to use shallow trays with hessian or wire netting bottoms.

Before drying, it is desirable to separate leaves and flowers from other unwanted plant members such as stems, which would slow down the process. Thus it is wrong to hang up bundles of peppermint or melissa tops, separating the leaves only when the whole is dry. Drying in bundles should be practised only when all the aerial parts are required (wormwood, centaury, marjoram, etc.) The commercial harvesting of bearberry, savin or rosemary on an economic scale is by collecting and drying the leafy branches; the leaves are then separated from the stems by beating and sieving.

The economics of commercial growing. The cultivation of medicinal plants is very labour intensive and if workers must be specifically engaged for this purpose the profit margin will be small. On the other hand, if the grower has available some accessory labour force (children, unskilled workers) he may hope for good profits. As an indication it may be said that the cultivation of medicinal plants will produce a return roughly similar to that of a market garden near a town.

For the cultivation of larger amounts it is necessary to have suitable buyers such as wholesale druggists, pharmacists, etc.

The collection of wild plants is generally less demanding than cultivation; but it is still necessary to be the proprietor of the land. Such collections are generally made by children or by unskilled persons. Regard must be paid to what has already been said above about collection and drying.

The following are some general rules to be observed:

1. Collect only those species that are abundant in the area: the collection of rare plants is an unjustifiable destruction of nature, moreover it gives a poor yield. The collected plants should always be handled with the greatest care.

2. Collect only a few species at one time in order to avoid accidental mixing that would make the collected material valueless.

3. Take the greatest care to ensure that no other plants are mixed in with any one collection.

4. Dry the plants as soon as possible after collection, especially leaves, flowers or entire plants. Aromatic plants should be dried as much as possible in the shade in a place with good circulation of air, the plants being spread out in thin layers; it is best if they do not overlap each other at all.

5. Artificial heat should be used only for plants that are without odour when fresh.
Aromatic plants should not be exposed to a temperature greater than 35° C (95°F); other plants, in general, may be dried at 50°-70° C (122°158°F), but this latter temperature may be too high even for plants without aromatic constituents; foxglove of optimum activity is obtained by drying at 25°C (77° F)

6. Thick roots should always be cut longitudinally before drying.

7. The dried drugs should be placed immediately into well dried containers (chests, metal boxes, sacks). They should not be handled roughly for they are readily broken.

8. Drugs containing volatile oils should not be stored in ordinary plastic boxes or sacks, for these materials absorb the volatile oils from the drugs, which are then volatilised from the external surface.