HISTORY OF DIFFERENT FOODSTUFFS IN BODY 1051 



associated with leucine and tyrosine, where it may be deposited in 

 the form of calcuH. 



Whatever intermediary stages the amino-acids may pass through, 

 they are finally converted -into carbon dioxid, water, and . relatively 

 simple substances containing nitrogen. Chief among the latter is urea 

 and its precursor ammonia, but there are also some which cannot be 

 regarded as members of the amino-acid group, such as creatine and 

 creatinine. These bodies are very largely the result of endogenous pro- 

 tein metabolism, although some of the creatine and creatinine of the 

 food may appear as such in the urine. Besides, some of the amino- 

 acids may appear in the urine as such, giving rise to the so-called amino- 

 nitrogen or undetermined nitrogen. But since the metabolism of the 

 cells also includes that of their nuclear material, and since the latter is 

 also ingested, for example, in the form of sweet-breads or thymus, this 

 list should be augmented to embrace the purin bodies. The determina- 

 tion of sulphur in the urine is valuable in so far as it gives a fair picture 

 of the metabolism of the proteins, because this foodstuff serves prac- 

 tically as the only vehicle for its entrance into the body. 



The purine bodies arise from purine. The first product of the 

 oxidation of this body is hypoxanthine from which adenine i« derived. 

 The second product of its oxidation is xanthine and its amino deriva- 

 tive guanine. The trioxypurine is uric acid, which in birds and reptiles 

 is the chief derivative of protein metabolism. Whether this substance 

 is also excreted by the mammals in important amounts is still a ques- 

 tion. ^ It would appear, however, that the urine acquires uric acid 

 and also a certain amount of purine bases after a copious diet of meat 

 and especially after the ingestion of glandular material. For this 

 reason, Burian and Schur^ have recognized an endogenous and exog- 

 enous purine metabolism, the former having to do with the reduction 

 of the purine of the tissues and the latter with that of the preformed 

 purine constituents of the food ingested. In general, it may be said 

 that the exogenous purine bears a close relation to the purine of the 

 urine. If it accumulates in the tissues it gives rise to the condition 

 known as gout, and hence, purine-rich food should not be taken by 

 persons who suffer from this metabolic difficulty or tendency (gouty 

 diathesis). More recently, it has also been shown by Ascoli and Izar^ 

 that purine may be synthetized in the mammalian body from urea and 

 carbon-rich residues, two molecules of the former uniting with a 

 carbon residue containing three carbon atoms. This purine would of 

 course be endogenous in its character. 



1 Jones, Nucleic Acid, Monographs in Biochem., Longmans, Green and Co., 

 1914. 



2 Zeitschr. physiol. Chemie, xxiii, 1897, 55. 



3 Ibid., xliii, 1911, 319., 



