METABOLISM IN NEPHKITIS 361 



whereas Ambard formulates these factors as follows: 

 (urea in the blood) 2 



rate of urea excretion 



= constant. 



A consideration of all the facts presented makes it seem probable that the 

 first ratio is more nearly correct. 



The Relation of Water Elimination to Urea Excretion. It has been 

 definitely established that an increased urine volume in a given unit of 

 time, that, is a diuresis, will increase the total output of solids in the urine. 

 It remained for Austin, Stillman and Van Slyke to determine the limita- 

 tions of this phenomenon. They found that an increase in the rate of 

 urine volume excretion up to a certain point varying between 2.5 to 6.0 

 liters in twenty-four hours result in a regular increase of urea output which 

 surpasses the rate which would be expected from the blood urea. In other 



rate of urea excretion 



words, the ratio ; -r ri T~ rises as the urine volume increases. 



urea in the blood 



Quantitatively this increase is approximately proportional to the square 

 root of the rate of urine volume excretion or 



rate of urea excretion 



: -: r-j - = constant V volume of urine. 



urea in the blood 



There is a limit beyond which a greater urinary flow will not increase the 

 urea elimination. This has been well termed the augmentation limit. The 

 augmentation limit is not the same in every individual. It varies from 2.5 

 to 6.0 liters in twenty-four hours in normal persons. Its value, when ap- 

 plied to renal affections, remains to be determined. Such 24 hour urinary 

 volumes (2.5 to 6 liters) are in excess of the urinary volume usually ob- 

 served in man. On the other hand, a marked lowering of the urinary flow, 

 as occurs in dehydration, will diminish the urea output (Marshall and 

 Davis) . If anuria results, because of fluid loss through other emunctories 

 than the kidneys, as in cholera, the rather curious phenomenon is presented 

 of absolute cessation of kidney activity while there is no impairment of 

 renal function, as far as the kidneys themselves are concerned. 



The Concentration of Urea in the Urine. Austin, Stillman and Van 

 Slyke claim that the concentration of urea in the urine has no definite 

 constant influence on the rate of urea excretion; it only becomes of im- 

 portance when the urinary volume is low. The urine volume appears to 

 be the determining factor as shown in the previous paragraph. Under 

 certain common pathological conditions, when the ability of the kidney 

 to concentrate the urine is markedly diminished, it is found that the 

 urine volume is the absolute controlling factor in the amount of urea 

 excreted inasmuch as the urinary urea concentration remains more or 

 less constant. Addis and Watonabe in their various publications have 

 stressed the independence of the value of Ambard's constant from the 



