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When red bark is extracted with dilute hydrochloric acid, the product filtered, and excess of sodium hydrate added thereto, quinine and quinidine are precipitated: on concentrating the mother liquor, cinchonine falls down, and on further concentration with addition of still more alkali, cinchonidine is thrown out.

The latest work on the action of these alkaloids has shown that cinchonine has a tendency to produce convulsions in certain patients, and that this action is a still more marked feature of cinchonidine and cinchonamine.

Quinidine is almost as powerful an antidote to malaria as quinine; cinchonidine has about two-thirds the power of quinine, and cinchonine less than one-half.

The British Pharmacopoeia directs that the bark, when used to make the various medicinal preparations, shall contain not less than 5 nor more than 6% of total alkaloids, of which at least one-half is to be constituted by quinine and cinchonidine.

A fourth alkaloid, cinchonidine, is isomeric with cinchonine, which yields it when boiled with amyl alcoholic potash, but is laevo-rotatory, slightly soluble in ether, and faintly fluorescent.