Cortex Azadirachtæ; Nim Bark, Margosa Bark.
Botanical Origin—Melia indica Brandis (M. Azadirachta L., Azadirachta indica Juss.), an ornamental tree, 40 to 50 feet high and attaining a considerable girth,[627] well known throughout India by its Hindustani name of Nim, or by its Portuguese appellation of Margosa.[628] It is much planted in avenues, but occurs wild in the forests of Southern India, Ceylon and the Malay Archipelago, as far as Java.[629]
The hard and heavy wood which is so bitter that no insect will attack it, the medicinal leaves and bark, the fruit which affords an acrid bitter oil used in medicine and for burning, the gum which exudes from the stem, and finally a sort of toddy obtained from young trees, cause the Nim to be regarded as one of the most useful trees of India.
M. indica is often confounded with M. Azedarach L., a native of China,[630] and probably of India, now widely distributed throughout the warmer regions of the globe, and not rare even in Sicily and other parts of the south of Europe. The former has an oval fruit (by abortion) one-celled and one-seeded, and leaves simply pinnate. The latter has the fruit five-celled, and leaves bipinnate.
History—The tree under the Sanskrit name of Nimba is mentioned in Susruta, one of the most ancient Hindu medical writings, composed perhaps about the 10th century of our era.
In common with many other productions of India, it attracted the notice of Garcia de Orta, physician to the Portuguese viceroy at Goa, and he published an account of it in his work on drugs in 1563.[631] Christoval Acosta[632] in 1578 supplied some further details and also a figure of the tree. The tonic properties of the bark, long recognized by the native physicians of India, were successively tested by Dr. D. White of Bombay in the beginning of the present century, and have since been generally admitted.[633] The drug has a place in the Pharmacopœia of India.
Description—The bark in our possession[634] is in coarse fibrous pieces about ⅕ of an inch thick and 2 to 3 inches wide, slightly channelled. The suberous coat is rough and cracked, and of a greyish rusty hue. The inner surface is of a bright buff and has a highly foliaceous structure. On making a transverse section three distinct layers may be observed—firstly the suberous coat exhibiting a large brown parenchyme interwoven with small bands of corky tissue,—secondly a dark cellular layer, and then the foliaceous liber. The dry bark is inodorous and has a slightly astringent bitter taste.
Microscopic Structure—The suberous coat consists of numerous layers of ordinary cork-cells, which cover a layer of nearly cubic sclerenchymatous cells. This latter however is not always met with, secondary bands of cork (rhytidoma) frequently taking its place. The liber is commonly built up of strong fibre-bundles traversed by narrow medullary rays, and transversely separated by bands of parenchymatous liber tissue. Crystals of oxalate of calcium occur in the parenchyme more frequently than the small globular starch grains. The structure of the bark varies considerably according to the gradual development of the secondary cork-bands.
Chemical Composition—Margosa bark was chemically examined in India by Cornish[635] (1856), who announced it as a source of a bitter alkaloid to which he gave the name of Margosine, but which he obtained only in minute quantity as a “double salt of Margosine and Soda” in long white needles.
From the bitter oil of the seeds he isolated a substance which he called Margosic Acid, and which he doubted to be capable of affording crystallizable salts. The composition neither of this acid nor of margosine is known, nor have the properties of either been investigated.
The small sample of the bark at our disposal only enables us to add that an infusion produced with perchloride of iron a blackish precipitate, and that an infusion is not altered by tannic acid or iodohydrargyrate of potassium. If the inner layers of the bark are alone exhausted with water, the liquid affords an abundant precipitate with tannic acid; but if the entire bark is boiled in water, the tannic matter which it contains will form an insoluble compound with the bitter principle, and prevent the latter being dissolved. It is thus evident that to isolate the bitter matter of the bark, it would be advisable to work on the liber or inner layers alone, which might readily be done, as they separate easily.
According to the recent researches of Broughton[636] the bitter principle is an amorphous resin soluble in the usual solvents and in boiling solutions of fixed alkalis. From the latter it is precipitated by acids, yet, probably, altered. Broughton ascribed the formula C₃₆H₅₀O₁₁ to this bitter resin purified by means of bisulphide of carbon, ether and absolute alcohol; it fused at 92° C. He obtained moreover a small quantity of a crystallized principle, which he believed to be a fatty body, yet its melting point of 175° C. is not in favour of this suggestion.
Uses—In India the bark is used as a tonic and antiperiodic, both by natives and Europeans. Dr. Pulney Andy of Madras has found the leaves beneficial in small-pox.
Cortex Swieteniæ; Rohun Bark.
Botanical Origin—Soymida[637] febrifuga Juss. (Swietenia febrifuga Willd.), a tree of considerable size not uncommon in the forests of Central and Southern India. The timber called by Europeans Bastard Cedar is very durable and strong, and much valued for building purposes.
History—The introduction of Rohun Bark into the medical practice of Europeans is due to Roxburgh[638] who recommended the drug as a substitute for Cinchona, after numerous trials made in India about the year 1791. At the same time he sent supplies to Edinburgh, where Duncan made it the subject of a thesis[639] which probably led to it being introduced into the materia medica of the Edinburgh Pharmacopœia of 1803, and of the Dublin Pharmacopœia of 1807.
Though thus officially recognized, it does not appear that the bark came much into use or by any other means fulfilled the expectations raised in its favour. At present it is regarded simply as a useful astringent tonic, and as such it has a place in the Pharmacopœia of India (1868).
Description—Our specimen of Rohun bark[640] which is from a young tree, is in straight or somewhat curved, half-tubular quills, an inch or more in diameter and about ⅕ of an inch in thickness. Externally it is of a rusty grey or brown, with a smoothish surface exhibiting no considerable furrows or cracks, but numerous small corky warts. These form little elliptic scars or rings, brown in the centre and but slightly raised from the surface. The inner side and edges of the quills are of a bright reddish colour.
A transverse section exhibits a thin outer layer coloured by chlorophyll, and a middle layer of a bright rusty hue, traversed by large medullary rays and darker wedge-shaped rays of liber. The latter has a fibrous fracture, that of the outer part of the bark being rather corky or foliaceous. The whole bark when comminuted is of a rusty colour, becoming reddish by exposure to air and moisture. It has a bitter astringent taste with no distinctive odour. The older bark frequently half an inch thick and fibrous, has a thick ragged corky layer of a rusty blackish-brown colour, deeply fissured longitudinally, and minutely cracked transversely. Old bark, according to Dymock (1877), is generally in half quills of a rich red-brown colour.
Microscopic Structure—The bark presents but few structural peculiarities. The ring of liber is made up of alternating prosenchymatous and parenchymatous tissue. In the latter the larger cells are filled with mucilage, the others with starch. The prosenchymatous groups of the liber exhibit that peculiar form we have already described as hornbast (p. 74); it chiefly contains the tannic matter, besides stellate crystals of oxalate of calcium which are distributed through the whole tissue of the bark. The medullary rays are of the usual form, and contain starch granules. The corky coat is built up of a smaller number of vaulted cells.
Chemical Composition[641]—The bitter principle of the bark has been ascertained by Broughton[642] to be a nearly colourless resinous substance, sparingly soluble in water but more so in alcohol, ether, or benzol. It does not appear to unite with acids or bases, and is less soluble in water containing them than in pure water. It has a very bitter taste, and refuses to crystallize either from benzol or ether. It contains no nitrogen. To this we may add that the bark is rich in tannic acid.
Uses—Rohun bark is administered in India as an astringent tonic and antiperiodic, and is reported useful in intermittent fevers and general debility, as well as in the advanced stages of dysentery and in diarrhœa.