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A TEXTBOOK OF PHYSIOLOGY 



A similar reaction takes place when sodium hypobromite is added 

 to urine, but nitrogen alone is evolved, the CO 2 remaining combined 

 to the alkali present in the solution. 



+ SNaBrO + 2NaHO = 3NaBr + N + 3HO + NaC0 3 . 



Advantage is taken of this reaction for estimating the daily output 

 of urea. The method is not very exact, since nitrogen is also evolved 

 from uric acid and other bodies present in the urine. A known amount 

 of urine is mixed with an excess of the hypobromite solution, and the 

 evolved nitrogen collected. The apparatus employed, such as Dupre's, 

 is generally graduated in percentages of urea. With Southall's ureo- 

 meter (Fig. 221) one c.c. of urine from a special pipette is carefully 

 injected below the bend of the tube which is filled with hypobromite. 

 If 110 such apparatus be available, the gas may be 

 collected over water in a burette, and the amount 

 of urea calculated from the fact that 0-1 gramme 

 of urea yields 354 c.c. of nitrogen. 



A more exact method of estimating urea in urine 

 is to heat some of the urine with magnesium chloride 

 and hydrochloric acid. The urea under these cir- 

 cumstances is broken down to ammonia, which 

 combines with the acid present to form ammonium 

 chloride. The other nitrogenous constituents of the 

 urine are not affected in the process. The amount 

 of ammonia in the ammonium chloride thus formed 

 is then determined by Kjeldahl's process. 



There is little information of cl.nical value to be 

 gained from an estimation of the urea output alone. 

 What is required is a knowledge of the amount of 

 nitrogen taken in the diet, and the relative values 

 of the urea, creatinine, ammonia, etc., excreted in 

 pathological conditions. Clinical information of this 

 character has yet to be collected. 



The precursors of urea and the site of its formation in the body 

 have already been discussed. About 25 to 40 grammes of urea are 

 excreted dai.y, the amount varying according to the diet. 



Uric Acid is the chief nitrogenous waste product of birds and 

 reptiles. It occurs also in mammalian urine combined with alkalies. 

 The empirical formula of uric acid is C.H 4 X 4 3 ; it is tri-oxy-purin, 

 and the formula may be graphically represented thus: 



HN CO 



FIG. 221. 

 UREOMETER. 



OC C NH 



HN C N 



CO 



(see p. 50). About 04 to 0-7 gramme of uric acid is excreted in 

 the human urine daily. It is a dibasic acid, and therefore forms two 



