51 6 PHYSIOLOGICAL CHEMISTRY 



end of 15 minutes aspirate for about one -half minute to remove any ammonia 

 present in the free condition in "A." After this aspiration, open "A" and 

 introduce 5 c.c. of saturated potassium carbonate. Close "A" at once and 

 aspirate until all the ammonia has been removed from "A" and carried over 

 into the acid in "B." The time needed for the aspiration varies for different 

 pumps from 5 to 30 minutes, and should be determined by trial for the par- 

 ticular apparatus used. At the end of the time needed for the aeration, 1 the 

 pump is dIBonnected (care being taken to avoid back suction) and the ex- 

 cess acid in "B" is titrated by means of fiftieth-normal alkali. 



Calculations. The number of cubic centimeters of fiftieth-normal acid 

 neutralized is multiplied by the factor 0.056 to give the number of grams 

 of urea-plus ammonia-nitrogen hi 100 c.c. of the urine. The ammonia 

 alone may be determined at the same time as the ammonia plus urea, using 

 the same technic except that 5 c.c. of the undiluted urine, no urease, and the 

 factor 0.0056 are used for the determination of ammonia alone. The am- 

 monia tubes are run hi the same series as those for the urea determination, 

 using the same air current for all. 



Interpretation. The mean average daily excretion of urea by normal 

 adults is usually placed at about 30-35 grams but is very closely de- 

 pendent upon the protein ingestion and hence may vary widely. It 

 is of significance only when the amount of nitrogen ingested is known 

 with some degree of accuracy. In disorders associated with increased 

 tissue catabolism as in fevers, the excretion of urea is increased. It 

 may be decreased in pronounced kidney and liver disorders due to 

 decreased formation and decreased power of elimination, but these 

 findings are not constant. 



The per cent of the total nitrogen of the urine occurring as urea 

 varies on the average from 80-90. On a high protein diet it is nearer 

 90 per cent; on a very low nitrogen but high calorie diet it may not 

 be over 60 per cent. In marked acidosis it may be considerably 

 decreased relative to the total nitrogen (see ammonia). 



(b) Youngburg's Modification of Van Slyke and Cullen's Method. 2 

 Principle. The ammonia of the urine to be analyzed is removed by 

 use of permutit, and urea is determined in the ammonia free filtrate 

 by the Van Slyke and Cullen procedure using the alcoholic urease 

 solution of Folin and Youngburg in place of the acetone insoluble 

 urease. 



Procedure. Dilute 5 c.c. of urine to 50 c.c. (10 to 50 if very dilute urine) 

 and mix well. Place 3 to 4 grams of dry permutit in a wide bottomed flask, 

 preferable a 200 c.c. or 250 c.c. volumetric, and add 20 to 25 c.c. of the diluted 

 urine. Agitate for 5 minutes. Allow to settle 15 to 30 seconds and pour through 



1 See Fiske (Jour. Biol. Chem., 23, 455, 1915) and Van Slyke and Cullen (Jour. Bid. 

 Chem., 24, 117, 1916) for discussion of details of method. 

 2 Youngburg, G. E.: Jour. Biol. Chem., 45, 391, 1921. 



