240 THE URINE. 



Instead of decomposing the silver compounds as described with 

 sodium sulphide, we may proceed as follows : the precipitate is 

 suspended in about 300 c.c. of acidulated water and subjected to a 

 current of hydrogen sulphide until the decomposition is complete ; 

 on subsequent boiling all the uric acid passes into solution, and can 

 be separated from the precipitate of silver sulphide by filtration. 

 Filtrate and washings are then further treated as described. 



Albumin and sugar, if present, must in either case be removed. 



The Xanthin Bases. 



The xanthin bases which have been found in the urine of man 

 are xanthin, hypoxanthin, guanin, carnin, paraxanthin, heteroxan- 

 thin, episarein, and under certain pathological conditions adenin. 

 Their amount, however, is always small, and normally constitutes 

 about 10 per cent, of the quantity of uric acid, viz., from 0.0^ to 

 0.06 gramme. Of this amount, from 0.02 to 0.03 gramme is repre- 

 sented by xanthin. Hypoxanthin and guanin probably stand next 

 in order, while paraxanthin and heteroxanthin are foimd only in 

 traces. From 10,000 liters of urine Kriiger and Salomon thus 

 obtained only 7.5 grammes of the latter. 



Origin. It has been shown that the xanthin bases are derived 

 from the nuclear nucleins, and are probably formed in all the tissues 

 of the body. There is reason to suppose, moreover, that a certain 

 fraction is referable to ingested nucleins. Under normal conditions 

 the greater portion of the xanthin bases is then, no doubt, oxidized 

 to uric acid, but a variable fraction escapes as such. To a certain 

 extent the oxidation to uric acid occurs in the liver, but, as I have 

 shown, this takes place also in other organs of the body, as both 

 xanthin bases and uric acid are obtained in transfusion experiments. 

 At the same tirrie it was noted that the relative amount of the two 

 was largely influenced by the degree of oxygenation of the blood, so 

 that xanthin bases only were obtained if venous blood was used, 

 while both were found when arterial blood was employed. We 

 can thus understand that, as a general rule, at least a certain rela- 

 tion exists in the elimination of uric acid and the xanthin bases, 

 A diminished elimination of the hitter is thus quite frequently 

 associated with a corresponding increase of the former, or vice raw, 

 and both may, of course, be increased or diminished together. The 

 most notable increase in their elimination is observed in leukaemia, 

 and here adenin also appears in the urine. 



Theobromin (dimethyl-xanthin) and eaifein (trimethyl-xanthin) 

 are partly eliminated in the urine as such, and partly appear as a 

 met nyl-xan thin which is apparently identical with heteroxanthin. 



Xanthin has once been found in crystalline form in a urinary 

 sediment, and has in several instances been encountered in vesical 

 calculi. 



As the isolation of the individual substances from the urine in 



