Thus thinned out and reduced in numbers, the list of species of Chinchonæ has been established by Dr. Weddell at nineteen, and two doubtful;[25] but even the classification of this eminent authority, published in 1849, already requires much alteration and revision. For instance: Dr. Weddell gives no place to the "red-bark" species, the richest in alkaloids, and one of the most important, which, through the recent investigations of Mr. Spruce, will now probably be admitted by botanists as a distinct species, the _C. succirubra_ (Pavon). A new grey bark now introduced into India as _C. Peruviana_ (Howard), and the _C. Pahudiana_ (Howard), a worthless kind, cultivated by the Dutch in Java, will also be received as additional species. It seems likely also that the _C. Condaminea_ requires to be divided into two or three distinct species; while the _C. Boliviana_ (Weddell) will sink into a mere variety of the _C. Calisaya_. The commercially valuable species, however, comprise but a small proportion of the whole; and, as all these have now been introduced into India, they alone deserve our attention. They are as follows:-- _C. succirubra_ (Pavon) yielding _Red bark._ {_C. Chahuarguera_ (Pavon) } _C. Condaminea._ {_C. crispa_ (Tafalla)} " _Crown bark._ {_C. Uritusinga_ (Pavon) } {_C. lancifolia_ (Mutis) " _Carthagena bark._ _C. nitida_ (Ruiz & Pavon)} _C. micrantha_ (Ruiz & Pavon)} " _Grey bark._ _C. Peruviana_ (Howard) } _C. Calisaya_ (Weddell) " _Yellow bark._ 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:-- I.--The Loxa region, and its _crown barks_. II.--The _red-bark_ region, on the western slopes of Chimborazo. III.--The New Granada region. IV.--The Huanuco region in Northern Peru, and its _grey barks_. V.--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.