i BIC ACID AND THE PI BINE BODIES 6 17 



be produced as a result of the combination of amino-malonic acid with 

 area, the amino-malonic acid being produced by condensation of hydro- 

 cyanic-acid molecules: 



:: HCN-» II X CH CN CO Ml — Ml CO 



I 

 CO CNB 



Ml CNH, 

 (hydrocyanic (amino malonic (urea) (oxy-diamino-pyrimid 

 acid) nitri 



Another possible source of pyrimidine is the oxidation of arginine to 

 guanidine-propionic acid, which then condenses to form amino pyrimi- 

 dine. 



Purine synthesis undoubtedly occurs in the mammalian body, but it 

 is difficult to recognize in metabolism investigations because it is a Blow, 

 continuous process. The probability of its occurrence, however, is indi- 

 cated by such results as those described on page 614, in which incr< 

 in purine excretion is observed after varying the intake of food, even 

 when this is itself entirely free from purine substances. Whether or not 

 changes in the activity of purine synthesis occur in conditions of dis< 

 is a question which awaits investigation. 



The Influence of Various Physiological Conditions, of Drugs, and of 

 Disease on the Endogenous Uric-acid Excretion. Muscular exercisi was 

 though.1 by Burian to cause an increased excretion of uric acid, from 

 which he drew the conclusion thai the hypoxanthine present in compara- 

 tively large amount in muscular extract, or its precursor, inosinic acid, 

 must be an importanl source of endogenous uric acid, other obsen 

 (Leathes, etc.) have found thai strenuous exercise causes a distinct in- 

 crease in uric-acid excretion, which, however, is much less marked on 

 repetition of the same kind of exercise on the next day. If Borne new 

 kind i>f muscular work is performed, another increase in uric acid will 

 result. There are still other investigators who deny that muscular work 

 has any influence "ii uric-acid excretion. 



It has been observed by several investigators that the endogenous 

 purine excretion is distinctly higher during tin- waking hours than during 

 sleep. This can nut he shown to depend on variations in the urinary 

 function, and since it is decidedly doubtful whether ordinary muscular 

 activity has any influence, the diurnal variation is most difficult 

 account for. The endogenous excretion in man is not the same for 

 diffen n? individuals, even when calculated for the same body weighl ; it 

 varies between 0.12 and 0.20 per cenl purine nitrogen in an adult man. 

 It remains remarkably constant for a given individual from time tn 

 time, being unaffected by moderate degrees of variation in the amount 



