534 PHYSIOLOGICAL CHEMISTRY 



the hot fluid by means of a filter-pump, wash with hot water, add 10 c.c. of 10 

 per cent hydrochloric acid and evaporate the filtrate in a porcelain dish until 

 the total volume has been reduced to about 10 c.c. Permit this residue to 

 stand about two hours to allow for the separation of the uric acid, leaving the 

 purine bases hi solution. Filter off the precipitate of uric acid, using a small 

 filter paper, and wash the uric acid, with water made acid with sulphuric acid, 

 until the total volume of the original filtrate and the wash water aggregates 

 75 c.c. Determine the nitrogen content of the precipitate by means of the Kjel- 

 dahl method (see page 504), and calculate the uric acid equivalent. 1 



Render the filtrate from the uric acid crystals alkaline with sodium hydroxide, 

 add acetic acid until faintly acid and heat to 7oC. Now add i c.c. of a 10 per 

 cent solution of acetic acid and 10 c.c. of a suspension of manganese dioxide 2 

 to oxidize the traces of uric acid which remain hi the solution. Agitate the mix- 

 ture for one minute, add 10 c.c. of the sodium bisulphite solution 3 and 5 c.c. 

 of a 10 per cent solution of copper sulphate and heat the mixture to boiling for 

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

 its nitrogen content by means of the Kjeldahl method (see page 504). 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 hi terms of nitrogen. 



Benedict and Saiki 4 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. 5 

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

 chemical colorimetric method for uric acid (see page 530). 



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

 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 



1 This may be done by multiplying the nitrogen value of three and adding 3.5 mg. 

 to the product as a correction for the uric acid remaining in solution in the 75 c.c. 



J Made by heating a 0.5 per cent solution of potassium permanganate with a little alco- 

 hol until it is decolorized. 



1 To dissolve the excess of manganese dioxide. 



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



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



