AMOUNT, COMPOSITION, \\i> CnARACTEB OP URINE 



solution containing an average of 1.00, or concentrates it at l< 



times. 



Urea. The chief of the nitrogenous bodies of the urine is urea, the 

 origin of which has been fully described in the chapters on metabolism. 

 No constituenl of the urine is Bubjecl to greater variation both in abso- 

 lute and in relative amounts. <>n an average diel containing 120 grains 

 of protein per day, the absolute urea excretion may amounl to aboul 30 

 grams; on a low protein diet it may be only a few grams. When the pro- 

 tein intake is high, the nitrogen eliminated as urea may be ! ,( » per cent 

 of the total nitrogen; but when the protein intake is low, this proportion 

 may fall to tin per cent. The difference is because on a low protein diet 

 the greater percentage of nitrogen eliminated is endogenous in origin, 

 and urea, which is the chief constituenl of the exogenous nitrogen mo 

 of the urine, is accordingly decreased on low diets. 



In recent years the importance of the relationship between the con- 

 centration of the urinary constituents in the blood and the urine has 

 been much insisted upon, and since the estimation of the amounl 



urea in the hi 1 and the mine is relatively simple, most of the work 



has been done by using these values. Ambard and Weil believe that a 

 quantitative relationship exists between the fate ■ * t" mine excretion and 

 t lie concentration of urea in the blood and the urine, since the urea in 

 the blood acts as a stimulus to the renal cells. By comparing the rate 

 of una excretion and the concentration of urea in the blood and urine 

 in a mathematical formula, they have obtained a value which they he- 

 lieve is more or less fixed for the normal kidney. This expression is 



known as Ambard's <■<>< l]ici< ni oml formula,* and has 1 n us^d as a 



means ..f evaluating the functional capacity of the kidney. 



Whatever tin- value of the formula may lie in expressing the relationship 

 existing between the rate of urea excretion and the concentration of this 

 sail in the blood, it is certain that, in diseased iditions where impair- 

 ment of tlie kidney is certain, the concentration of urea in the blood 

 mains permanently at an abnormally high average level, although I 



ibard and \V< U'a formula i-: 



IV 



K , in which: 



\V 



D — x 



P 



K 



D = output ol 



P - weight of the patient. 



' f urine. 



itandard weight 



the urine. 



The average value for tl 

 Critical review - of the « u k I 

 w tanabe.' 



