Peruvian or Jesuits' Bark, is the dried bark of several species of the genus Cinchona, belonging to the Linnean class and order Pentandria Digynia, and to the natural order Cinchonaceae. (See BOTANY, vol. v., p. 196.) This bark has for a couple of centuries retained its reputation as a nearly infallible remedy or specific in the cure of agues or intermittent fevers. It is not known how the native Peruvians first acquired the knowledge of the virtues of this bark, though many stories are told to account for it; such as, that a native was cured of an ague by drinking from a pool into which a cinchona tree had fallen, to the water of which it had imparted its virtues, &c. But if certain natives had so discovered its virtues, the knowledge of this must not have spread far, as even a century after its reputation was established in Europe, Humboldt and Bonpland found the natives around Loxa, whence the best supplies were derived, still ignorant of its value in agues. Its virtues were first made known in Europe in the year 1640 in consequence of its having cured of an intermittent fever the wife of the viceroy of Peru, the Conde del Chinchon; and from this circumstance the bark was afterwards known as the bark of Chinchon, Cortex Chinchonae, variously corrupted, according to the pronunciation, into Chinchona, Kinchina, Quinquina. Shortly after its introduction into Spain, the Jesuits had the bark sent to them by their brethren in Peru, and keeping the secret of its source to themselves spread it over Europe. In consequence of its being alone procurable through the Jesuits, it received the name of Jesuits' bark. On its first introduction into Europe it was vehemently opposed by the medical profession, till its cause was espoused by Dr Roland Sturm of Antwerp in 1659. An Englishman of the name of Talbot having discovered its source a few years later, and succeeded in curing with it the Dauphin of France, the Prince of Condé, and many persons of rank—sold his secret to the French government for a knighthood, L1,600, an annuity of L80, and a monopoly of the trade for ten years. Its price at this time reached the enormous sum of L5 sterling per ounce.

For more than a century after the discovery of its virtues the jealousy of the Spaniards foiled all attempts to investigate the botanical history of the cinchona barks; and even at the present day, notwithstanding the investigations of La Condamine, Jussieu, Ruiz and Pavon, Humboldt and Bonpland, Poppig, and even the latest naturalist who has visited these regions, Weddell, much remains to be ascertained regarding the species of trees which yield the several varieties of bark. Weddell has done more than others to determine accurately the exact species which yield several of the varieties of bark; and has, in addition to the external characters of the barks, given in his elaborate work drawings of the appearance of fine sections of the several barks under the microscope. The subject has been still further investigated in this country by John Eliot Howard, Esq.; and it is to be hoped that in a few years the whole of the different varieties of bark will be able to be referred to their proper species. Chemistry now lends a powerful aid to all such investigations; for as the essential and powerful remedial agent in these barks is found to reside in an alkaloidal substance, which in the most valued barks is termed quinine, the less valued barks are found to contain less of this and a greater proportion of a less valued alkaloid, cinchonine; or the quinine is quite superseded by another similar principle called aricine.

The cinchona trees are met with in the elevated valleys of the Andes, in Colombia, Peru, and Bolivia, from the 11th degree of N., to the 20th degree of S. latitude, and from 1200 to 10,000 feet above the level of the sea. The bark is collected from May to November. The trees are usually cut down and peeled; and the fresh shoots which spring from the roots are ready for cutting after six or eight years. The Indians, however, to save themselves trouble, often peel the bark from the tree while still standing, and so destroy the tree for ever. The thinner bark from the small branches curls up in drying, and forms quilts; the thicker bark from the larger branches and stems remains in flat pieces.

The curative properties of Peruvian bark depend on the presence in the bark of peculiar alkaloidal substances, which vary in quality and kind in the different varieties of barks. The most valued of these is quinine; and hence in modern medicine this substance, combined with sulphuric acid, when it forms the sulphate of quinine, has almost entirely superseded the use of the bark itself in the cure of agues and other diseases. Other alkaloidal principles, similar but scarcely so powerful in action, exist in the cinchona barks, as cinchonine, aricine, cinchovatine, quinidine, &c. All these have more or less powerful febrifuge properties; and the first especially might with propriety be substituted for the more expensive quinine in hospital and dispensary practice, and in the army and navy. So much have these chemical preparations of the bark superseded the use of the crude bark itself; that the latter is now very rarely used in medical prescriptions; while these alkaloidal principles, from their small bulk, from their not overloading the stomach with a great mass of inert matter, and from their unvarying uniformity of strength, may be given in doses and in cases where the crude bulky powder could not be used. Almost every disease which shows a tendency to recur in regular fits or paroxysms is alleviated or removed by the use of Peruvian bark, or of its alkaloids quinine and cinchonine. Hence the value of these not only in agues (intermittent fevers), but in neuralgia, tic douloureux, hooping-cough, &c. Quinine and cinchonine are also powerful tonics, and are given with the best effects in recovery from debilitating fevers and diseases, in gangrene, &c.