This section is from the book "A Text Book Of Materia Medica, Being An Account Of The More Important Crude Drugs Of Vegetable And Animal Origin", by Henry G. Greenish. Also available from Amazon: A Text Book of Materia Medica : Being an Account of the More Important Crude Drugs of Vegetable and Animal Origin.
The coca shrub, Erythroxylum Coca, Lamarck, and E. truxillense, Rusby (N.O. Lineœ) has been cultivated in Peru and Bolivia for so long that the plant is not known in the wild state. It is cultivated also in Java and formerly to a limited extent in Ceylon. The dried leaves are in almost daily use in Peru and Bolivia as a nerve-stimulant; mixed with lime or with the ashes of a species of Cheno-podium and chewed they impart unusual powers of endurance, allaying the cravings of hunger and the feeling of fatigue. On the steep sides of the valleys in the spurs of the Andes the coca is cultivated in large quantities. The leaves are picked twice in the year, or sometimes oftener, and dried. Only a very small proportion of the coca produced is exported; by far the greater part is consumed by the natives, whilst a considerable quantity is used in Callao for the manufacture of cocaine, the crude alkaloid being exported instead of the leaves.
Fig. 14. - Bolivian coca leaf. a, upper surface, showing the prominent veinlets; b, under surface, showing the lines on each side of the midrib. Natural size.
The following are at present the commercial varieties of coca leaves: -
1. Bolivian or Huanuco (E. Coca).
2. Peruvian or Truxillo (E. truxillense).
3. Java (E. truxillense).
Bolivian coca leaves are usually fairly intact. They are brownish green in colour, and oval in outline, varying usually from 4 to 8 cm. in length and from 2'5 to 4 cm. in breadth. Both surfaces are glabrous, and the lateral veins and veinlets are distinctly prominent. The margin is entire, and the lamina tapers towards both base and apex; the latter is acute, the midrib projecting in the form of a minute horny point (apiculus) which, however, is frequently broken off.
The midrib is reddish brown, depressed on the upper surface and surmounted by a raised ridge; on the under surface on either side of the midrib a distinct, raised, curved line runs from the base to the apex of the leaf. This line is formed in the young leaf, each half of which is inrolled (involute) in the bud and forms a ridge closely applied to a similar ridge on the other half. Although the leaf is not thick it is by no means fragile, the lateral veins and veinlets being comparatively strong, and hence prominent on the upper surface (fig. 15). When a transverse section is examined under the microscope most of the epidermal cells of the under surface will be seen to project in the form of small papillae; in surface view these appear as circular rings.1 This peculiarity, although exhibited by other species of
Fig. 15. - A, under surface of Bolivian coca leaf; B, of Peruvian coca leaf, showing the difference in the veinlets. Magnified.
Erythroxylum, is so unusual as to render it of considerable diagnostic importance. The leaves have a faint but characteristic odour. The taste is slightly bitter, followed by a feeling of numbness in the mouth and throat. The small, oblong-ovoid, dark brown, pointed fruits are occasionally found in the drug.
Peruvian or Truxillo coca leaves are rather smaller than the Bolivian; they are pale green in colour and are more fragile, hence they are usually more or less broken. On the under surface the two curved lines are much less distinct; on the upper surface the ridge above the midrib is less marked; on the under surface the veinlets are less prominent and the midrib green in colour. These leaves frequently contain an admixture of the carefully picked and dried flowers of a species of Inga easily recognised by their yellowish brown, tubular, hairy calyx and numerous deep red filaments forming a plume; this is an intentional addition, made apparently with the view of improving the coca, and is not an adulteration. The pale, reddish brown fruits of the coca are also occasionally to be found.
1 Compare Greenish and Collin, Anatomical Atlas, p. 63.
The plant that yields this variety of coca has been distinguished as E. truxillense, Rusby.
Java coca is exported in the form of coarse powder; it does not reach the English market, but is used in Holland and Germany for the extraction of cocaine.
The student should observe in both Bolivian and Peruvian coca leaves:
(a) The curved lines on the under surface of the leaf,
(b) The minute horny apiculus,
(c) The characteristic odour and taste; in the Bolivian leaves:
(d) The brownish green colour, prominent veinlets, and less broken appearance,
(e) The ridge above the midrib; in the Peruvian leaves:
(/) The pale green colour, broken appearance, and less prominent veinlets, (g) The absence of a distinct ridge over the midrib.
Coca leaves contain several alkaloids, the most important of which is cocaine, C17H11N04, which forms colourless monoclinic prisms with a bitter, benumbing taste. Bolivian leaves contain more of this alkaloid than the Peruvian, but the quantity is usually less than 1 per cent. Other alkaloids of less importance are cinnamyl-cocaine and a- and β-truxilline (isotropylcocaine, cocamine, isococamine); these are frequently present in Peruvian leaves in larger quantities than cocaine. All these alkaloids are easily hydrolysed, and they all yield, together with other products, a crystalline alkaloid, ecgonine, from which by suitable treatment cocaine can be regenerated. Thus cocaine, when hydrolysed, yields methyl alcohol, benzoic acid, and ecgonine; cinnamyl-cocaine yields methyl alcohol, cinnamic acid, and ecgonine; and truxilline yields methyl alcohol, truxillic acid, and ecgonine. Ecgonine is very closely allied to tropine; a-truxilline is a powerful heart-poison. (See under 'Belladonna-Leaves.')
In leaves imported from Java benzoyl-pseudotropine or tropa-cocaine has been found; this alkaloid yields, when hydrolysed, benzoic acid and pseudotropine; the latter is isomeric with tropine. This variety of coca contains about 0.7 per cent, of total alkaloid; it also contains four yellow, crystalline glucosides.
Coca leaves contain, in addition, cocatannic acid.
Moisten 5 gm. of the finely powdered leaves with 2 per cent, solution of ammonia; pack in a long, narrow percolator, percolate with ammoniated ether until 100 c.c. have been collected or the drug is exhausted. Shake out with 2 per cent, hydrochloric acid till exhausted. Mix the acid solutions, wash once with ether, make alkaline with ammonia, and shake out with ether. Allow the mixed ethereal solutions to evaporate, dry at 100° and weigh.
Coca is a stimulant tonic and restorative, and is used during convalescence. Cocaine hydrochloride, when administered hypo-dermically, or applied to an exposed mucous surface, rapidly paralyses the sensory nerves and thus produces local anaesthesia. It is therefore of great value and much used in minor surgical operations of the eye, nose, ear, etc.