506 PHYSIOLOGICAL CHEMISTRY 



Interpretation. An adult of medium size on a mixed diet will usually 

 excrete 12-18 grams of nitrogen per day. It varies, however, almost 

 directly with the protein ingestion and hence usually runs parallel to 

 the excretion of urea (see page 516). In a normal adult the total 

 nitrogen of the feces and of the urine will often be almost exactly 

 equal to the total nitrogen of the food. Such a condition is called 

 "nitrogen equilibrium. 7 ' The feces usually contain very little nitrogen. 

 (See also Ammonia, Creatinine, etc.) 



Calculation of Percentage Nitrogen Distribution. In modern metabo- 

 lism studies where the various forms of nitrogen are determined, in 

 addition to the total nitrogen as yielded by the Kjeldahl method, it is 

 customary to indicate what portion of the total nitrogen was present in 

 the form of each of the individual nitrogenous constituents. These 

 percentage values are secured by dividing the weight (grams) of 

 nitrogen excreted for the day in the form of each individual nitrogenous 

 constituent by the weight of the total nitrogen output for the same 

 period. For example, if the total nitrogen excretion is 9.814 grams 

 and the excretion of urea-nitrogen is 81520 grams and the excretions 

 of nitrogen in the forms of ammonia and creatinine are 0.271 gram and 

 0.639 gram respectively, the percentage distribution for these forms of 

 nitrogen would be calculated as follows: 



8. 5 20 grams urea-nitrogen -T- 9.814 grams total nitrogen = 84.3 per cent 



0.271 gram ammonia-nitrogen -f- 9.814 grams total nitrogen = 2. 7 per cent 

 0.639 gram creatinine-nitrogen * 9.814 grams total nitrogen = 6. 5 per cent 



Nitrogen Partition in Urines Containing Albumin. If the urine to 

 be tested contains albumin this must be removed before an attempt at 

 a nitrogen partition is made. This may be done by heating to boil- 

 ing, acidifying with acetic acid to coagulate the protein, filtering and 

 making up the filtrate to the original volume of the urine. If very small 

 amounts of albumin are present this is attended with difficulty. In 

 these cases Tracy and Welker 1 have suggested the use of aluminium 

 hydroxide cream. It apparently removes none of the nitrogenous con- 

 stituents of normal urine. 



Procedure. One liter of urine (containing not over i per cent of albumin) 

 is mixed with one liter of- aluminium hydroxide cream 2 and filtered. 



2. Folin-Wright Simplified Macro-KjeldahlMethod. 3 Principle 

 The method differs from the Kjeldahl procedure in that the digestion 



1 Tracy and Welker: Jour. Biol. Ghent., 22, 55, 1915. For other applications of alu- 

 minium hydroxide precipitation of colloids, see Welker and Marshall, /. Am. Chem. Soc. t 

 25, 820, 1913. 



* Aluminium Hydroxide Cream. To a i per cent solution of ammonium alum at room 

 temperature add a slight excess of a i per cent solution of ammonium hydroxide. Wash by 

 decantation until the wash water shows only the faintest trace of residue on evaporation. 

 Stronger solutions should not be used. 



3 Folin and Wright: Jour. Biol. Chem., 38, 461, 1919. 



