CHEMICAL BASIS OF THE ANIMAL BODY. 185 



be made to yield urea by treatment with boiling dilute sulphuric acid 

 or baryta water. NH : C (NH 2 ) 2 + H 2 O = (NH 2 ) 2 CO + NH 3 . Further, 

 it affords a connecting link between the xanthin series and kreatin 

 (p. 143), the latter substance being, as already stated, methylguanidin- 

 acetic acid, while guanidin is itself the chief product of the oxidation of 

 guanin. 



It may be readily synthetised in several ways ; of these its 

 formation by the action of alcoholic ammonia on chlorpicrin (tri- 

 chlornitromethan) CC1 S (NO 2 ) or on cyanogen iodide shows clearly its 

 constitution. In the first case 



CC1 8 (NO 2 ) + 3NH 3 = NH : C (NH 2 ) 2 + 3HC1 + HNO 2 . 



In the second CNI + 3NH 3 = NH : C (NH 2 ) 2 + NH 4 I, or in other words 

 guanidin may be regarded as a compound of cyanamide and ammonia 

 CJST . NH 2 + NH 3 - NH : C (NH 2 ) 2 . The relationship to kreatin may 

 now be at once made evident by comparing the reaction just given 

 with that for the synthesis of kreatin from cyanamide and sarkosin : 



CN . NH 2 + CH 2 . NH (CH 3 ) . COOH = NH : C 



N(CH 3 ).CH 2 .COOH. 



Xanthin derivatives. 



The monomethyl (?) derivative of xanthin (heteroxanthin) has already been 

 described, as also one of the possible dimethyl derivatives, viz. paraxanthin. 



When the (silver or) lead salt of xanthin (PbC 5 H 2 N 4 2 ) is dried and heated in 

 sealed tubes at 100 with methyl iodide, iodide of lead is formed together with 

 dimethyl-xanthin 1 . The substance thus obtained is identical with theobromin, 

 long known as the characteristic alkaloidal constituent of cocoa-beans, the fruit of 

 Theobroma cacao. A third presumably dimethyl derivative of xanthin has recently 

 been described as occurring in tea, viz. theophyllin 2 . When the silver salt of 

 theobromin is further treated as above with methyl iodide it is converted into 

 methyl- theobromin or trimethylxanthin, which is identical with the vegetable 

 alkaloid, long known under the synonymous names of theme or caffeine, as 

 occurring in the leaves or seeds of many plants such as tea and coffee, also in the 

 Brazilian ' guarana ' prepared from the fruit of Paullinia sorbilis, in ' mate ' of 

 South America, an infusion of the leaves of Ilex Paraguayensis, in kola-nuts used 

 as food in Central Africa (the fruit of Serculia acuminata), in South African 'bush- 

 tea,' and in many other plants from which stimulating beverages are obtained by 

 infusion 3 . Apart from tbe close chemical relationship of the alkaloidal principles 

 of the above plants to the nitrogenous crystalline extractives ' of muscles, it is 

 interesting to notice further that they seem to bear the same general relationship to 

 the organisms in which they respectively occur. There can be but little doubt that 

 the xanthin bodies (and uric acid) are typically products of the downward, 

 excretionary nitrogenous metabolism of animals. The alkaloidal principles of 



1 E. Fischer, loc. cit. (sub xanthin). 



2 Kossel, Zt. f. physiol. Chem. Bd. xin. (1889), S. 298. 



3 Of. Johnston and Church, Chem. of common life, 1880, p. 147. 



