224 LECTURE XII. 



and it is probable that something of the same kind may 

 take place in the plant, the bodies formed being alkaloids 

 instead of urea and uric acid. As a matter of fact, certain 

 vegetable alkaloids, thei'n and theobromine, are allied to uric 

 acid. Further, Broughton has observed that when the 

 Cinchona is manured with highly nitrogenous substances, the 

 amount of alkaloids is very much increased : this is a parallel 

 to the well-known fact that when an animal consumes a large 

 quantity of nitrogenous food, the excretion of urea and of 

 uric acid is increased. 



The alkaloids are of two kinds, namely those which do and those 

 which do not contain oxygen. To the former group belong the more 

 familiar alkaloid such as morphin (Ci 7 H 19 NO 3 ) and the other opium-alka- 

 loids ; theobromin (C 7 H 8 N 4 O 2 ), thein (C 8 H 10 N 4 O 2 ), strychnin (C n HaaN a Oj), 

 atropin (CwHagNOj), quinin (C 2 oH 24 N 2 O 2 ) : to the latter belong mercurialin 

 (CH 6 , N) probably identical with methylamin (CH 3 , H 2 N), coniin 

 (C 8 H 15 N), nicotin (C 10 H 14 N 2 ), and spartei'n (C^H^Ns). It has been found 

 that an alkaloid which contains no oxygen can be obtained from one which 

 does : thus Wertheim has succeeded in preparing coniin (C 8 H 15 N) from 

 conydrin (C 18 H 17 ON). It appears that most of the alkaloids can be 

 traced to the compound ammonia pyridin (C 5 H 6 N). The alkaloids occur 

 in plants in combination with organic acids. 



We have every reason to believe that the alkaloids are in 

 reality waste-products, that is, substances which cannot enter 

 into the constructive metabolism of the plant, for the obser- 

 vations of Knop and Wolf shew that the demand for com- 

 bined nitrogen cannot be met by supplying the plant with it 

 in the form of alkaloids, although, as we have seen (p. 124), 

 the plant can take up urea, uric acid, leucin, tyrosin, or gly- 

 cocoll. 



There is one point which deserves especial mention before 

 we leave this subject, namely this, that, as a rule, the nitro- 

 genous metabolism of plants is not accompanied by any loss 

 of nitrogen when the conditions are normal. In this respect 

 plants differ widely from animals. This difference is due 

 partly to the fact (p. 159) that plants are endowed with a 

 greater constructive capacity than animals ; animals excrete 

 the amides formed in the destructive metabolism of the 

 organism in the form of urea, uric acid, etc., whereas plants 



