Quinine (C12H24N202) is one of many alkaloids obtained from the bark of the Calisaya-tree (Fig. 176) and related species. Its great and widely recognized value in the treatment of malaria is explained by the fact that in quantities not seriously injurious to a human being the alkaloid acts as a deadly poison upon minute parasites which occur in the blood of malarial patients and are regarded as the cause of the disease. It is highly valued also as a tonic. Its intensely bitter taste is a property familiar to most persons.

Fig. 176. Calisaya tree (Cinchona Calisaya, Madder Family, Rubiaceoe). A, flowering branch, B, flower. C, corolla and stamens. D, fruit. E, fruit with upper half of wall removed to show the packing of the seeds. E, fruit, cut across. G, seed, enlarged, and cut through the embryo, lengthwise. (Luerssen.) Tree about 12 m. tall; leaves pale green; flowers pink; fruit dry. Native home, Andes of Peru.

Fig. 176.-Calisaya-tree (Cinchona Calisaya, Madder Family, Rubiaceoe). A, flowering branch, B, flower. C, corolla and stamens. D, fruit. E, fruit with upper half of wall removed to show the packing of the seeds. E, fruit, cut across. G, seed, enlarged, and cut through the embryo, lengthwise. (Luerssen.)-Tree about 12 m. tall; leaves pale green; flowers pink; fruit dry. Native home, Andes of Peru.