This book is a sequel to the monograph Medicinal Plants in Nigeria, written in 1960 (Oliver, 1960), which was a critical survey of the scattered information available about drug plants found in Nigeria; it suggested a first choice of the plant material which seemed potentially most important, and made suggestions concerning points requiring further scientific investigation (constituents, pharmacology, etc.).
As medical science develops and becomes more organized in the West African countries, the time would seem to have come to reassemble and update our knowledge of the subject and extend it to the whole of tropical West Africa. Furthermore, greater importance is now being attached to the use of locally available medicines as a means of reducing reliance on expensive imported drugs.
Since the first book appeared, a number of papers dealing with the chemical analysis, pharmacology and clinical action of West African plants have been published. Supplementary information now available about individual plants will be included here, and the range of plants considered can thus be more selective. This time an attempt is made to classify the drugs according to their established or possible medical uses, this being the best way of rapidly assessing the medical interest of any particular drug.
The value of a drug will depend on several factors:
(1) whether it is the only drug, or one of the few drugs, used in the treatment of a disease;
(2) whether the disease in the treatment of which it is used is a common one;
(3) whether it is less toxic than other existing drugs for a particular purpose;
(4) whether it can be produced more cheaply than alternative drugs used in treating the same disease.
This last criterion may hold good for plants grown for other commercial uses (fibres, timber, fixed oils (liquid fats or fatty oils), essential oils, gums, resins, etc.), for in such cases the drug may be available as a by-product, with a substantial cut in production costs.
The following points, which were mentioned in my earlier publications, still hold good:
(a) Recognized drug plants which also grow in West Africa and are officially listed in various Pharmacopoeias or are already in use elsewhere have to be checked by well-established methods to ascertain whether the yield in active constituents of the plant when grown in West Africa reaches a suitable standard. If it does, the plant can, if not indigenous, be grown on a greater scale and the relevant drugs produced by standard procedures.
(b) The therapeutic action of a plant depends on its chemical constituents and can often be forecast and easily investigated pharmacologically if these constituents are known.
(c) The botanical relationship of a particular plant to well-known drug plants, or to plants containing therapeutically active constituents, may be an indication of a potential therapeutic interest. Indeed, chemical relationship, based on secondary substances specifically found in certain genera and families, has been observed and is made use of in botanical taxonomy. Several genera of one botanical family may thus have a similar action. Many Solanaceae contain alkaloids with a parasympatholytic action, and many Labiatae contain essential oils, while cardiac heterosides are often found among the Asclepiadaceae and Apocynaceae.
(d) As many plants found in tropical West Africa also grow in other areas of similar climate, such as parts of India, Sri Lanka and Indonesia, their use in such countries will require investigation too. However, an attempt ought to be made to ascertain whether the African plants have the same constituents in equivalent quantities, and the same properties, for in these other countries the content of active principles may not be the same. Such differences may be attributed to differences in climate, soil or other ecological conditions, but are more likely to be due to varying degrees of enzymatic destruction of the chemical principles (Debray, 1966, p. 51, quoted in Oliver-Bever, 1968).
(e) Local medicinal usage may provide useful information about lesser-known plants. Unfortunately, local uses can be very numerous and often differ completely from one tribe to another for one and the same plant. It should not be forgotten that superstition plays a considerable part in folk medicine. Vesicants, purgatives, diuretics and emetics are often used because they 'oppose strong action' or 'expel evil influences'. However, the herbalist is sometimes right and then his medicine has to be investigated further.
In some cases certain local plants are used in the same way by many different tribes, or for similar ailments in other parts of the world where such plants are also found. This would seem to make this use more likely to be accurate. It could, however, be empirical and might be based, for instance on the 'Law of Signatures', which has adepts among several under-developed peoples existing without contacts. Hence in 1960 the local uses indicated for tropical West Africa (Dalziel, 1937) were compared with the uses to which the same species are put in India (Chopra et al., 1956), Sri Lanka (Jayaweera, 1945, 1952, 1954), Indonesia (van Steenis-Kruseman, 1953), the Ivory Coast (Kerharo and Bouquet, 1950), Ghana (Irvine, 1930), Senegal
(Sébire, 1899; Chevalier, 1905-13), Guinea (Pobéguin, 1912), the Congo (Staner and Boutique, 1937), Nigeria (Holland, 1908-29), Africa in general (Githens, 1949), etc. This resulted in a fairly rigorous selection of local medicinal uses and this information was partly made use of in the preparation of the present text. Some interesting indications may thus well have been overlooked, but a rapid survey of the existing knowledge seemed to be the first requirement. More detailed and more up-to-date information on local medicinal uses can be found in the 'Mémoires' published by the Office de la Recherche Scientifique et Technique Outre Mer (ORSTOM) (see e.g. Bouquet, 1969) in Kerharo and Adam (1974) and in Ayensu (1978). These latter books (and some of the others) also give the vernacular names of the plants they deal with.
Throughout the text, the phrase 'plants acting on . . .' is used as convenient terminology for 'plants whose leaves (or roots, extracts, active principles, etc.) act on . . .' . The chapters themselves are named on the basis of the physiological system affected.
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