URINE . 515 



three minutes. Filter off the precipitate, wash it with hot water, and determine 

 its nitrogen content by means of the Kjeldahl method (see page 483). Inas- 

 much as the composition and proportion of the purine bases present in urine is 

 variable, no factor can be applied. The result as regards these bases must 

 therefore be expressed in terms of nitrogen. 



Benedict and Saiki 1 report cases in which the total purine nitrogen by this 

 method was less than the uric-acid nitrogen as determined by the Folin-Shaffer 

 method. The inaccuracy was found to lie in the Kriiger and Schmidt method. 

 To obviate this they advise the addition of 20 c.c. of glacial acetic acid for each 

 300 c.c. of urine employed, the acid being added before the first precipitation. 



Interpretation. The amount of purine bases excreted by a normal 

 man is small and variable. Values from 16-60 mg. have been found. 

 The purine base nitrogen is of course only a fraction of this. The 

 amount excreted is influenced by the diet somewhat in the same way 

 as is the excretion of uric acid being also increased in disorders asso- 

 ciated with increased uric acid excretion such as leukemia. The purine 

 bases form a higher percentage of the total purine excretion in the case 

 of the monkey, sheep, and goat than in the case of man. 



2 . Hunter and Givens' Modification of Kriiger-Schmidt Method. 2 

 Principle. The Kriiger-Schmidt process is combined with the micro- 

 chemical colorimetric method for uric acid (see page 510). 



Procedure. The first copper-purine precipitate as obtained in the Kriiger- 

 Schmidt procedure is suspended in about 200 c.c. of water, to which there is 

 added about i c.c. of concentrated hydrochloric acid. The mixture is vigorously 

 boiled, whereupon the whole or greater part of the precipitate goes into solution. 

 Removal of the copper is effected by treatment with hydrogen sulphide in the heat, 

 and excess of the sulphide is completely expelled by. renewed boiling. Filtration 

 under suction, and thorough washing of flask and filter result in a filtrate which 

 is perfectly clear and nearly colorless. This is concentrated if necessary, and 

 made up to a convenient volume which must of course be sufficiently large to 

 retain, when cool, the uric acid in solution. t)f this an aliquot part is utilized 

 directly for the colorimetric determination of uric acid. In the remainder the 

 residual uric acid is destroyed and bases determined according to the regular 

 Kruger-Schmidt procedure. This modification is recommended particularly 

 where the amount of uric acid present is minute. 



3. Welker's Modification of the Methods of Arnstein and of Salkowski. 3 

 Principle. The phosphates are removed by treatment with magnesia mixture. 

 The purine bases and uric acid are then thrown down as their silver salts and the 

 nitrogen content of this precipitate determined. 



Procedure. Four hundred c.c. of urine, free from protein, are treated with 

 100 c.c. of magnesia mixture and 600 c.c. of water. This is then filtered and of the 

 clear filtrate a measured quantity (600-800 c.c. )is treated with an excess (10 c.c.) 

 of a 3 per cent silver nitrate solution. Concentrated ammonium hydroxide is 

 added in small quantities, with stirring, until all the chlorides have dissolved. 



1 Benedict and Saiki: Jour. Biol. Chem., 7, 27, 1909. 



2 Hunter and Givens: Jour. Biol. Chem., 17, 37, 1914. 



3 Dittman and Welker: New York Med. Jour., May-June, 1909. 



