The bark of an undetermined South American tree. (Aniba coto (Rusby) Kosterm. -Henriette)
History.—Coto bark is exported from the interior of Bolivia, but the tree from which it is derived is unknown. (The bark of Palicourea densiflora, Martius, is known in Brazil under the name Coto-coto). In 1875, Dr. Wittstein received a few pounds for chemical examination, with the statement that it was produced by a species of Cinchona; this was disproved, however, by Harz, after a microscopic examination. In this country, coto bark and not Para-coto bark (see below), in substance, in tincture, or in fluid extract, is always used in medicine.
Description.—Coto bark reaches us in pieces of from 4 to 12 inches in length, 2 to 4 inches in width, and from 1/2 to 3/4 inch in thickness; the outer or corky portion is about 1/16 of an inch in thickness, dark-brown internally, rusty upon the inner surface, and externally grayish-brown or blotched with spots of white. The surface is somewhat rough. Beneath the thin cork it is of a dark-cinnamon color; fibrous upon its inner surface and intermixed with some granular matter; but, toward the outer part the granular matter increases in proportion until the reverse is true. Its fracture presents very numerous points of a golden yellow. The odor of the bark is aromatic, especially when freshly broken, reminding one of mace or of a mixture of mace and cinnamon. The taste is intermediate between that of mace and allspice, finally becoming acrid and biting. The dust is irritating when inhaled.
Chemical Composition.—Dr. Wittstein found this bark to contain a pale-yellow, aromatic, volatile oil, of less density than water, and biting to the taste; a volatile alkaloid resembling propylamin, and two resins, besides a tannin, starch, formic, butyric, and acetic acids, etc. In 1876, Jobst obtained a crystallizable body, cotoin, possessing the biting taste peculiar to the bark, and which he supposed represented its medicinal virtues. Cotoin was obtained by exhausting the powdered bark with cold ether, distilling the greater part of the solvent, treating with light petroleum benzin, 6 parts (which caused the precipitation of a copious amount of resin), and evaporating the benzin solution to the point of crystallization. Afterward, by the same process of isolation, he found another crystalline, but non-pungent body in another sample of bark (since named Para-coto bark), and named it paracotoin. Still further examinations by Jobst and Hesse gave conflicting results, and later researches by the same chemists demonstrated that the discrepancies were due to the fact that two barks were upon the market under the name coto, and that only to the first, that examined by Wittstein, should the term (Coto) be applied; PARA-COTO BARK being accepted as the name of the second (see Related Drug).
Coto bark, according to the investigations of Jobst and Hesse (Lieb. Annal., Vol. 199, 1879, pp. 17-96; also see Amer. Jour. Pharm., 1880, pp. 20-28), contains cotoin and dicotoin, the latter occurring in the mother liquors from the preparation of cotoin, and being regarded as its anhydride. Cotoin forms square prisms of a light yellowish-white color, having an intensely biting taste, and melting at 130° C. (266° F.). The dust of cotoin causes violent sneezing and coughing. It is soluble in alcohol, ether, acetone, chloroform, carbon disulphide, and boiling water, and nearly insoluble in cold water. It is soluble in alkalies and alkaline carbonates, being again precipitated by mineral acids, and even carbonic acid gas. Its aqueous solution reduces gold and silver salts in the cold, and exhibits some characteristic color reactions with nitric and sulphuric acids, ferric chloride, etc. Its formula is C22H18O6, and tribromine- and triacetyl substitution products were obtained by the authors.
Action, Medical Uses, and Dosage.—Coto bark, in the form of powder, tincture, or extract, has been successfully employed in diarrhoea; M. von Gietl considered it a specific in the several forms of diarrhoea. Burkhart and Rieker have found it to possess extraordinary virtues in intestinal catarrh, diarrhoea, and dysentery. Good results are obtained from it in some cases of cholera infantum, and strong endorsement has been accorded it as a remedy to control the colliquative sweats of phthisis. It has likewise been employed beneficially in colic, dental nervous pains, in gout, and in rheumatism. The tincture made by percolating 1 part of the coarsely powdered bark with 9 parts of alcohol, may be given in doses of 10 drops, repeated every 2 hours; the powder, in doses of 1/2 grain, repeated 4, 5, or 6 times a day. The effects of the tincture and the powder are, however, very disagreeable, owing to the essential oil and the resinous principles present in them, producing a persistent, burning taste in the mouth, with increased flow of saliva, a burning sensation in the stomach, with eructations and vomiting, on which account the active principle, cotoin, has been substituted, as it does not occasion these unpleasant symptoms, and is fully as efficient. Cotoin is especially useful in cases in which opium and its preparations are contraindicated; its dose is very small, thus: In 4 fluid ounces of distilled water dissolve 7/10 of a grain, or 1 1/5 grains of cotoin, and to this add 10 drops of alcohol and 1 ounce of syrup. The dose is a tablespoonful every 1 or 2 hours.
Related Drug.—PARA-COTO BARK. Para-coto bark resembles coto bark in its general appearance, but has a much weaker odor, and only a faintly pungent, acrid taste. It reaches market under the name Coto, and is packed in exactly the same manner, thus, it is said, rendering its substitution in commerce frequent. The principal constituents are, paracotoin, which crystallizes from an ethereal tincture of para-coto bark, in yellowish scales, and has the composition C19H12O6. Solution of hydrate of potassium, or of sodium converts it into paracotoic acid (C19H17O7). Leucotin, a substance crystallizing in white prisms, is present in larger proportion, and is obtained by agitating the crystalline mass resulting from evaporation of the tincture of para-coto bark with glacial acetic acid. The leucotin dissolves in the acetic acid, and may be purified by recrystallization from hot diluted alcohol. Its composition is C34H32O10. Oxyleucotin is obtained from the alcoholic mother liquor, after separation of paracotoin, and has the composition, C34H32O12. An agreeable volatile oil was also obtained by distillation of the bark with superheated steam, colorless, specific gravity 0.9275, and separable into 5 distinct compounds by means of fractional distillation, with boiling points ranging from 160° C. (320° F.) to 242° C. (467.6° F.). In addition to the foregoing, several other products were identified, e. g., dibenzoyl hydrocotoin (C32H32O8), hydrocotoin (C15H14O4), and piperonylic acid (C8H6O4), and we refer the reader, if interested, to the original article, or the abstracts published in the Amer. Jour. Pharm., and in New Remedies, January, 1880 (see under Coto Bark; also see Ciamician and Silber, Chem. Centralbl., 1892. Vol. I, p. 751).