188 MEDICINAL AND POISONOUS PLANTS 
from the bark of the Calisaya-tree (Fig. 176) and related 
species. Its great and widely recognized value in the treat- 
ment 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 
Fic. 176.—Calisaya-tree (Cinchona Calisaya, Madder Family, Rubiacee). 
A, flowering branch, 3. B, flower. C, corolla and stamens. D, fruit. 
E, fruit with upper half of wall removed to show the packing of the 
seeds. F, 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. 
the blood of malarial patients and are regarded as the cause 
of the disease. It is highly valued also as a tonic. Its in- 
tensely bitter taste is a property familiar to most persons. 
Strychnine (C.,H..N.O.), the principal alkaloid obtained 
from the seeds of the nux vomica tree (Fig. 177), is one of 
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