146 MANUAL OF POISONOUS PLANTS 



only is the fundamental nucleus different in the two classes of alkaloids, but 

 groups that enter into these nuclei are different, thus leading to a large number 

 of possible compounds. To this group of alkaloids belong especially the alka- 

 loids of opium. For example, morphin, thebain, narcotin, narcein, papaverin, 

 and codein. There are also hydrastin, hydra^tium and berberin. 



THE PURIN GROUP OF ALKALOIDS. 



These compounds are not properly included with the alkaloids but they 

 belong with the purin compounds or xanthin bases. The nucleus (purin) or 

 atomic framework, shown by Fischer to characterize the xanthin bases, such as 

 uric acid, the xanthin derivatives, guanin and adenin, is found in caffein, theo- 

 bromin, theo-phyllin, compounds that are yet classed with the alkaloids. The 

 structural and mutual relationship of these to each other and to the xanthin bases 

 has been determined synthetically and hence their classification is not a doubt- 

 ful question. The alkaloids are methyl xanthins. Caffein is a tri-methyl xan- 

 thin and theo-bromin and theo-phyllin are di-methyl xanthins, the latter being 

 an isomer of theo-bromin. The alkaloid of tea is sometimes called thein al- 

 though its identity with the caffein of coffee has been recognized for a long 

 time. 



There are several alkaloids whose structural relations have not been deter- 

 mined. Among these are pilocarpin, colchicin, and physostigmin. For the des- 

 cription of these alkaloids see statement in this text under their appropriate 

 heads. 



PHYSIOLOGICAL ACTION OF ALKALOIDS AS DETERMINED 

 BY THEIR STRUCTURAL COMPOSITION. 



It is within comparatively recent time that pure alkaloids have been pre- 

 pared and consequently that their physiological effects could be determined. 

 Some of these like quinin were prepared in a fairly pure condition during the 

 first half of the last century but most of them belong to a later period. Atten- 

 tion has been called to the fact that a single alkaloid is rarely produced by the 

 plant and hence in the usual extracts from the plant there are several alka- 

 loids with varying physiological effects. These constitutents vary in amount 

 according to a variety of conditions under which the plant may produce them. 

 Acordingly the extracts of such plants will vary in the proportion of the alka- 

 loid present. For example, in cinchona bark the amount of quinin may vary 

 from 2 to 13 percent. The physiological effect of the cinchona extracts will be 

 markedly different in such extremes of composition, i. e. in reference to the 

 alkaloid quinin. 



In 1869, Crum, Brown, and Frazer called attention to the relation of the 

 structure of organic compounds to their physiological effects. They were 

 studying the comparative action of strychnin and brucin and although their 

 knowledge of the structure of these two compounds was not complete yet they 

 were able to trace a relation in this case. They found that the presence of 

 methyl or ethyl groups strongly affected the active properties of these com- 

 pounds. For example, brucin is regarded as the dimethoxy-deriative of strych- 

 nin. The discovery that most alkaloids are built about three nuclei, namely 

 pyridin, quinolin, and iso-quinolin added new zest to the study of the physiolo- 

 gical effects of certain organic groups when substituted in organic compounds. 



Quinolin is a strong antipyretic and antiseptic but produces other results 



