URINE AND ITS CONSTITUENTS. 713 



from the exogenous protein metabolism, and the total quantity is 

 thereby largely affected by the diet. It is increased by a meat diet, 

 as is the total nitrogen output ; it is decreased in fever. In disease 

 of the two organs most concerned with urea elimination, the liver 

 (formation) and the kidney (excretion), it is usually, though not always, 

 decreased. 



The quantitative estimation of urea in urine may be effected by 

 various methods, of which but one will be mentioned, because it re- 

 quires less time and less skill in manipulation than most other 

 methods. This determination is based upon the fact that urea is 

 decomposed by alkali hypobromites into carbon dioxide, water, and 

 nitrogen : 



CO(NH 2 ) 2 + 3(NaBiO) = SNaBr + CO, + 2H 2 O + 2N. 



The liberated nitrogen is collected, and from its volume the weight 

 of the urea is calculated. The carbon dioxide is absorbed by the 

 excess of alkali present. The hypobromite solution must be prepared 

 freshly by making the following mixture of: 



(a) 1 volume of a solution containing bromine, 125 grammes ; 

 sodium bromide, 125 grammes; water, 1 liter. 



(6) 1 volume of 22.5 per cent, sodium hydroxide solution. 



(c) 3 volumes of water. 



2NaOH + 2Br = NaBr + NaOBr -t H 2 O. 



Of the many instruments recommended for the determination of urea, the 

 latest modification of Doremus' apparatus (Fig. 74) is most convenient. The 

 operation is carried out thus : Some urine is poured into B, while the stopcock 

 C is closed and then opened for a moment so as to fill its lumen. After having 

 washed the tube A with water, it is filled with the hypobromite solution. From 

 the tube B, previously filled with urine. 1 c.c. (or less if much urea is present) 

 is allowed to mix with the hypobromite solution, and after the reaction is com- 

 pleted the reading is taken. The degrees marked upon the tube A indicate 

 directly the number of grammes of urea contained in -the quantity of urine 

 employed. 



Albumin must be removed, if present, and for careful work the specimen 

 must contain not more than 1 per cent, of urea, which can be readily accom- 

 plished by diluting a second specimen. 



For careful work this method is not sufficiently accurate, and the Folin 

 method should be used. 



Experiment 96. Determine urea in urine by the above-described methods. 



Ammonia in the urine. Ammonia is normally present in the 

 urine in small amount, representing about 5 or 6 per cent, of the total 

 nitrogen. The amount seems dependent upon two factors : the ability 

 of the organism to convert the waste nitrogen from the proteins into 



