THE NITROGENOUS EXCRETION. URINE. 367 



Solutions of urates in presence of alkali exhibit a reducing 

 action toward copper, silver and certain other salts, which fact 

 possesses an importance which will be explained later. 



XANTHINE AND THE OTHER PURINES. 



The amount of these purines not changed to uric acid is small, the sum 

 of all of the nitrogen so held not being over one-tenth of the uric acid 

 nitrogen, according to most observers. They are but slightly soluble in 

 pure water, but dissolve readily with alkali hydroxides to form compounds 

 like the urates. With the heavy metals the combinations are mostly 

 insoluble. 



PYRIMIDINE DERIVATIVES. 



Among the decomposition products of nucleinic acids the so-called 

 pyrimidines should be referred to, as they must bear some relation to the 

 urinary nitrogen. Pyrimidine itself represents a nucleus like purine from 

 which various derivatives may be formed. The relations as outlined by 

 Kossel are these : 



! N=C H 6 NH C=O NH CO 



II II II 



2 CH C H 5 C=O C H C=O C CH 3 



II II I II I II 



3 N C H 4 NH C H NH CH 

 Pyrimidine, C 4 H 4 N, Uracil, C 4 H 4 N 2 O 2 Thymine, C 5 H 6 N 2 O 2 



2, 6-dioxy pyrimidine 5-methyl uracil 



We have no definite knowledge of the occurrence of these bodies in 

 urine, but they are among the compounds which should be expected to 

 result from the nuclein metabolism and possibly form a part of the nitro- 

 gen residue not fully accounted for. Thymine has been obtained as a 

 well-crystallized compound, soluble readily in warm water. It is identical 

 with the body formerly described as nucleosin. 



CREATININE. 



Creatinine, C 4 H 7 N 3 O, is the anhydride of the creatine de- 

 scribed under the head of the muscle extractives, and is always 

 present in normal urine. The amount in which it occurs is 

 indicated by the analyses given above. Much has been writ- 

 ten on the question of the relation of creatine to urea, but the 

 evidence for the view held by some writers that the latter is 

 derived from the former is not very convincing. In a labora- 

 tory way by boiling creatine with baryta water, urea, sarkosine 

 and several other things result. But no corresponding reac- 



