METABOLISM IN NEPHRITIS 363 



mains to be determined. In many cases the coefficient of Ambard is of 

 very great help ; it is not infallible and it is a test that requires much time 

 and painstaking attention to detail. 



It is found that the coefficient of urea secretion shows better than 

 normal figures in fever, hyperthyroidism, and in the early stages of chronic 

 nephritis. Lewis attributes these in part to increased metabolic activity 

 of the kidney and other tissues, characteristic of fever and augmented thy- 

 roid secretion, and in part to the irritability of the kidney which, according 

 to Schlayer, is a sign of slight involvement of the kidney. These facts 

 concerning Ambard's constant are paralleled by similar findings in regard 

 to phthalein and water excretion. 



It is interesting to note from Lewis' work how in very severe nephritis 

 the coefficient of urea excretion is modified by one predominating influence, 

 the amount 'of water excreted, and is largely independent of the concen- 

 tration of urea in the blood. In the far advanced cases of chronic Bright's 

 disease the concentration of urea in the urine is often an absolutely fixed 

 quantity regardless of the volume of urine or of the level of the blood urea. 

 Under these circumstances it becomes obvious that Ambard's Constant 

 will vary : 



(1) directly as the blood urea (when the urea concentration in the 

 urine and volume of urine both remained fixed) 



(2) indirectly as the volume of urine (the urea concentration in the 

 urine remains fixed, but the urinary volume varies) 



Lewis demonstrates some beautiful examples of these possibilities. 

 Under these circumstances, it is evident that the volume of urine is the 

 last compensating factor to give way as renal insufficiency progresses. 

 This is extremely important to bear in mind from the therapeutic point 

 of view when treating the symptom complex of retention of waste prod- 

 ucts in nephritis. 



The Chloric! Threshold in Nephritis 



Ambard and Weill formulated certain laws by which they estimated 

 the chlorid threshold of the kidneys. These have been interpreted by Mc- 

 Lean^,) as follows: "Ambard and Weill applied laws to the excretion of 

 sodium chlorid in human subjects. They found that the same general 

 laws were applicable to sodium chlorid and to urea, with the important 

 exception that, while excretion of urea occurs no matter how low its con- 

 centration in the blood falls, there is a threshold for chlorid excretion, and 

 when the concentration in the plasma falls below this threshold value, ex- 

 cretion of chlorid practically ceases. In view of the fact that there is a 

 wide difference in chlorid content of the corpuscles and plasma, plasma 

 alone, as the fluid part of the blood, has been studied. Ambard and Weill, 



