URINE 493 



urease must not exceed 2 mg. This procedure has been found useful where small 

 quantities of urea are to be estimated. 



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 8090. 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). 



(c) Marshall's Urease Method. 1 Principle. This is a simple clin- 

 ical method for the determination of urea in urine. It differs from the 

 preceding method in that instead of aspirating off the ammonia formed 

 from the urea by the action of the urease, it is titrated directly in the 

 urine mixture, thus simplifying the procedure. The method is nearly 

 as accurate as the preceding, for normal urine the error being only 

 about 2 per cent which is very satisfactory for a rapid clinical procedure. 

 For diabetic urines the aeration procedure should be used as such urines 

 contain substances which render the titration inaccurate. 



Procedure. Two 5 c.c. portions of the urine are measured into flasks of 

 200-300 c.c. capacity and diluted with distilled water to about 100-125 c.c. 

 One c.c. of a 10 per cent solution of urease prepared as described on page 491 is 

 added to one flask, a few drops of toluene to each and the solution allowed to 

 remain, well stoppered, at room temperature over night (or five hours). The 

 fluid in each flask is titrated to a distinct pink color with N/io hydrochloric acid 

 using methyl orange as an indicator. A few cubic centimeters of the enzyme 

 solution used should also be titrated to determine the amount of N/io hydro- 

 chloric acid required to neutralize i c.c. 



Calculation. The amount of hydrochloric acid required for the contents of 

 the flask containing the urine and enzyme solution, less the amount used for 

 5 c.c. of urine alone and that previously determined for i c.c. of enyzme solution, 

 corresponds to the urea originally present in the sample of urine. Since i c.c. 

 of N/io HC1 is equivalent to 3 mg. of urea, the number of cubic centimeters 

 required, multiplied by 0.6 gives the value of urea expressed in grams per liter 

 of urine. 



Interpretation. See above. 

 1 Marshall: Jour. Biol. Chem., 14, 283, 1913. 



