The simpler natural bases / by George Barger.

  • George Barger
Date:
1914
Catalogue details

Licence: Public Domain Mark

Credit: The simpler natural bases / by George Barger. Source: Wellcome Collection.

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    practical definition is to describe a base as a substance which is pre¬ cipitated by phosphotungstic acid. Adopting this criterion we consider creatinine to be a base but creatine not. Alkaloid.—Some writers have used this term to include all natural bases, but the objections to this are evident from what has been said above, and the word is best restricted to complex vegetable heterocyclic bases derived from pyridine, quinoline, etc.1 There is no doubt as to what is generally meant by an alkaloid, but nevertheless a rigid definition is almost impossible. On the one hand narceine, for instance, is a typical alkaloid from opium, but the nitrogen atom does not form part of a ring; narceine is an amine. On the other hand histidine and its derivatives are not classed as alkaloids, although they contain the heterocyclic glyoxaline ring, which is also present in pilocarpine. The latter substance is an undoubted alkaloid. In a few cases the inclusion of bases in this monograph is arbitrary ; thus hordenine, which is usually called an alkaloid, has been included on account of its relationship to tyrosine ; ephedrine, which is isomeric with hordenine, has been ex¬ cluded. All betaines have been included, for no typical alkaloid shows a betaine structure. One further point should be noted. The typical alkaloids are generally found only in one or a few closely related species, but the simpler natural bases, in accordance with their close connection with proteins and phosphatides, have generally a much wider distribution. Ptomaine was originally applied by Selmi to bases from corpses and afterwards became identical with putrefaction base (Brieger). Some writers have restricted the term to poisonous bases. Lately it has fallen into disuse. Leucomaine was a term used by Gautier for animal bases such as creatinine, which are not formed by putrefaction ; this term is now quite obsolete. Toxins are poisonous bacterial products which when injected cause the production of anti-bodies, neutralising their poisonous properties ; an example is diphtheria toxin. Gautier has applied the word, in a different sense, to simple poisonous putrefaction bases. 1 Winterstein and Trier define plant alkaloids as nitrogenous substances which can no longer be utilised for building up protein. Thus they would call betaine an alkaloid.
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