ALKALOIDS form an important class of substances discovered by modern chemistry. They are divided into two classes—namely, natural and artificial. The natural A. are found in plants and animals, and are often designated organic bases. Those obtained from plants are likewise called They are composed essentially of carbon, hydrogen, and nitrogen ; besides which, the greater number contain oxygen. The A. have generally an energetic action on the animal system, and hence are every day employed in small doses as medicine ; whilst in comparatively large doses they are powerful poisons. They have, although in low a degree, the characteristic alkaline properties on vegetable colors, etc.; have generally a bitter acrid taste ; and form the active principles of the plants in which they are found. Such are morphia, codeine, and narcotine, found in opium ; quinine and chinconine, in chincona bark ; strychnine, in nux-vomica ; hyoscyamine, in henbane ; nicotine, in tobacco ; piperine, in black pepper ; caffeine or theme, in coffee and tea, etc.
The animal A. are few in number, the more important being urea, found in the urine of the mammalia ; and kreatine and kreatinine, two of the constituents of the juice of flesh. The artificial A. are those organic bases which are not found in any known plant or animal, but of which the later researches of chemists have contrived to form a large number. As the artificial A. do not differ essentially from the natural A. in composition. structure, or properties, it is confidently believed that the day is not far distant when all of the A. will be prepared artificially; indeed, recently several of the natural A. have been manufactured on the small scale without the intervention of the living plant or animal. For instance, urea can be formed from the simplest form of dead organic nitrogenous matter.
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