These species yield five different kinds of medicinal barks, which are collected from five different regions in South America; and in the following chapter I propose to give a brief account of each of these regions, of their chinchona-trees, and of the investigations of botanists down to the time when measures were taken to introduce these inestimable plants into Java and India. Such an account will naturally divide itself into five sections:—

  1. —The Loxa region, and its crown barks.
  2. —The red-bark region, on the western slopes of Chimborazo.
  3. —The New Granada region.
  4. —The Huanuco region in Northern Peru, and its grey barks.
  5. —The Calisaya region, in Bolivia and Southern Peru.

Before entering on this subject, however, it will be well to cast a hasty glance at the progress of those investigations which ended in the discovery of the febrifugal principle in Peruvian bark.

The roots, flowers, and capsules of the chinchona-trees have a bitter taste with tonic properties, but the upper bark is the only part which has any commercial value.[26] The bark of trees is composed of four layers—the epiderm, the periderm, the cellular layer, and the liber or fibrous layer, composed of hexagonal cells filled with resinous matter and woody tissue. In growing, the tree pushes out the bark, and, as the exterior part ceases to grow, it separates into layers, and forms the dead part or periderm; which in chinchonas is partially destroyed, and blended with the thallus of lichens. The bark is thus formed of the dead part, or periderm, and the living part, or derm. On young branches there is no dead part, the exterior layers remaining entire, while the inner layers have not had time to develop. In thick old branches, on the contrary, the periderm or dead part is considerable, while the fibrous layer of the derm is fully developed. In preparing the bark the periderm is removed by striking the trunk with a mallet, and the derm is then taken off by uniform incisions. The thin pieces from small branches are simply exposed to the sun's rays, and assume the form of hollow cylinders, or quills, called by the natives canuto bark. The solid trunk bark is called tabla or plancha, and is sewn up in coarse canvas and an outer envelope of fresh hide, forming the packages called serons.

The character of the transverse fracture affords an important criterion of the quality of the bark. Cellular tissue breaks with a short and smooth fracture, woody tissue with a fibrous fracture, as is the case with the calisaya bark. The best characteristics by which barks containing much quinine may be distinguished are the shortness of the fibres which cover the transverse fracture, and the facility with which they may be detached, instead of being flexible and adhering as in bad barks. Thus, when dry calisaya bark is handled, a quantity of little prickles run into the skin, and this forms one of its distinguishing marks.[27]

Until the present century Peruvian bark was used in its crude state, and numerous attempts were made at different times to discover the actual healing principle in the bark, before success was finally attained. The first trial which is worthy of attention was made in 1779 by the chemists Buguet and Cornette, who recognised the existence of an essential salt, a resinous and an earthy matter in quinquina bark. In 1790 Fourcroy discovered the existence of a colouring matter, afterwards called chinchona red, and a Swedish doctor named Westring, in 1800, believed that he had discovered the active principle in quinquina bark. In 1802 the French chemist Armand Seguin undertook the bark trade on a large scale, and found it necessary to study the means of discovering good barks, and distinguishing them from bad ones. He found that the best quinquina bark was precipitated by tannin, while the bad was not precipitated by that substance. In 1803 another chemist found a crystalline substance in the bark which he called "sel essentiel fébrifuge" but it was nothing more than the combination of lime with an acid which was named quinic acid. Reuss, a Russian chemist, in 1815, was the first to give a tolerable analysis of quinquina bark; and about the same time Dr. Duncan of Edinburgh suggested that a real substance existed as a febrifugal principle. Dr. Gomez, a surgeon in the Portuguese navy, in 1816, was the first to isolate this febrifugal principle hinted at by Dr. Duncan, and he called it chinchonine.[28]

But the final discovery of quinine is due to the French chemists Pelletier and Caventou, in 1820. They considered that a vegetable alkaloid, analogous to morphine and strychnine, existed in quinquina bark; and they afterwards discovered that the febrifugal principle was seated in two alkaloids, separate or together, in the different kinds of bark, called quinine and chinchonine, with the same virtues, which, however, were much more powerful in quinine. It was believed that in most barks chinchonine exists in the cellular layer, and quinine in the liber, or fibrous layer; but Mr. Howard has since shown that this view is quite incorrect.[29] In 1829 Pelletier discovered a third alkaloid, which he called aricine, of no use in medicine, and derived from a worthless species of chinchona, growing in most of the forests of Peru, called C. pubescens.[30]

The organic constituents of chinchona barks are—

Quina.¦ Kinovic acid.
Chinchonia.¦ Chinchona red.
Aricina.¦ A yellow colouring matter.
Quinidia.¦ A green fatty matter.
Chinchonidia.¦ Starch.
Quinic acid.¦ Gum.
Tannic acid.¦ Lignin.