THE ALKALOIDS. 



The term vegetable alkaloids was originally applied to the group 

 of basic substances (hence the name alkaloid), which were found in 

 plants, to distinguish them from basic substances (amines, formerly 

 ptomaines or toxines) found in animals, formed mainly by putrefaction. 

 The term alkaloid is now applied only to the basic substances occurring 

 in plants which contain in their constitution either a pyridine, quinoline, 

 isoquinoline, or pyrrole or pyrrolidine ring, or several rings. They are 

 classified according to the ring into the following groups : 



I. Pyridine group : 



Piperine, coniine, trigonelline (p. 151), nicotine. 



II. Pyrrolidine group : 



Hygrine, stachydrine (p. 150). 



III. Tropane group : 



Atropine, hyoscyamine, hyoscine, cocaine. 



IV. Quinoline group : 



Quinine, cinchonine, strychnine, brucine. 



V. Isoquinoline group : 



Narcotine, narceine, morphine, codeine, papaverine, 

 berberine. 



The constitution of most of the alkaloids is known, but some are 

 still under investigation. The details of the work upon the elucida- 

 tion of their constitution are very complex. Only the formulae of the 

 chief compounds can therefore be given so as to show their relation- 

 ship to pyridine and the other nuclei. 



The alkaloids generally occur in plants in the form of salts with 

 organic acids, such as citric, tartaric, malic, oxalic, succinic. They 

 are liberated from the salts by means of alkali and can frequently be 

 extracted from the alkaline solution by means of chloroform, ether 

 and other organic solvents. Most of the alkaloids are solid compounds ; 

 coniine, nicotine and a few others are liquid. They generally con- 

 tain oxygen in their composition, but again there are exceptions. 



