INTRODUCTION AND SCOPE. 



THE substances described in this monograph do not constitute a 

 homogeneous group, like the proteins or carbohydrates, and the choice 

 of a title was therefore difficult. Many are derived in various ways 

 from the amino-acids of protein, a few are constituents of phosphatides ; 

 some are of bio-chemical interest on account of their wide distribution 

 in animals and in plants, others are important because of their phy- 

 siological action. 



It is common to nearly all the simpler natural bases, however, that 

 they are insoluble in ether and chloroform and readily soluble in 

 water, so that their isolation is generally more difficult than that of 

 the complex vegetable alkaloids, which can be extracted by making 

 the aqueous solutions of their salts alkaline and then shaking with a 

 solvent immiscible with water. The separation of the simpler bases 

 from each other and from non-basic substances like peptones must be 

 carried out by means of suitable precipitants and crystalline derivatives. 

 The special technique required for this purpose constitutes the chief 

 bond between the bases with which we are here concerned. This 

 technique was first elaborated in a systematic manner by Brieger, who 

 employed mercuric chloride in the isolation of putrefaction bases. 

 The introduction of phosphotungstic acid, by Drechsel, as a general 

 precipitant for basic substances and its use for preparative purposes 

 marked a great advance ; later Kossel added the silver method for the 

 separation of imino-bases, such as arginine and histidine. Since then 

 the details of technique have been chiefly elaborated in three centres. 



Schulze at Zurich, in a long series of researches on plant bases, 

 discovered phenylalanine and arginine and more lately extended our 

 knowledge of betaines. Kutscher and his pupils, in Germany, have 

 isolated bases from a variety of sources, and Gulewitsch, at Moscow, 

 has studied exhaustively the bases in meat-extract. 



The history of the simpler natural bases has been greatly influenced 

 by the need of special methods for their isolation. Another influence, 

 adverse to their study, was the presence of alkaloids in drugs and 

 stimulants, which directed attention to these complex bases having 

 obvious physiological actions rather than to simpler bases of more 



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