These materials are in different proportions according to the barks. Grey bark chiefly contains chinchonine and tannin; Calisaya, or yellow bark, much quinine, and a little chinchonine; red bark holds quinine and chinchonine in nearly equal proportions; while the barks of New Granada chiefly contain chinchonidine and quinidine. The two latter alkaloids were definitively discovered in 1852 by M. Pasteur; although the Dutch chemist Heijningen had, in 1848, found what he called β quinine or quinidine. Chinchonidine is only second to quinine itself in importance as a febrifugal principle.
Quinine is a white substance, without smell, bitter, fusible, crystallized, with the property of left-handed rotatory polarization. The salts of quinine are soluble in water, alcohol, and ether. Of all the salts the bisulphate of quinine is preferred, because it constitutes a stable salt, easy to prepare, and containing a strong proportion of the alkaloid. It is very bitter and soluble, and crystallizes in long silky needles. It is prepared by adding sulphuric acid to the sulphate.[31]
Chinchonine differs from quinine in being less soluble in water, and being altogether insoluble in ether. It has the property of right-handed rotatory polarization.
Quinidine also has the property of right-handed rotatory polarization, and forms salts like those of quinine. It becomes green by successive additions of chlorine and ammonia.
Chinchonidine has not the property of turning green, and forms a sulphate almost exactly like sulphate of quinine.[32]
The discovery of these alkaloids in the quinquina[33] bark, by enabling chemists to extract the healing principle, has greatly increased the usefulness of the drug. In small doses they promote the appetite and assist digestion; and chinchonine is equal to quinine in mild cases of intermittent fever; but in severe cases the use of quinine is absolutely necessary. Thus these alkaloids not only possess tonic properties to which recourse may be had under a multitude of circumstances, but also have a febrifugal virtue which is unequalled, and which has rendered them almost a necessary of life in tropical countries, and in low marshy situations where agues prevail. Many a poor fellow's life was saved in the Walcheren expedition by the timely arrival of a Yankee trader with some chests of bark, after the supply had entirely failed in the camp.[34] Dr. Baikie, in his voyage up the Niger, attributed the return of his men alive to the habitual use of quinine; and the number of men whose lives it has saved in our naval service and in India will give a notion of the vast importance of a sufficient and cheap supply of the precious bark which yields it. India and other countries have been vainly searched for a substitute for quinine, and we may say with as much truth now as Laubert did in 1820—"This medicine, the most precious of all those known in the art of healing, is one of the greatest conquests made by man over the vegetable kingdom. The treasures which Peru yields, and which the Spaniards sought and dug out of the bowels of the earth, are not to be compared for utility with the bark of the quinquina-tree, which they for a long time ignored.[35]
CHAPTER II.
The valuable species of Chinchona-trees—their history, their discoverers, and their forests.