It has been the practice of clinicians for many years to treat cases of nephritis by means of a dietetic therapy, in which the various forms of nitrogen-containing food have beeen much restricted. One of the several reasons for curtailment of protein in the dietary has been that a damaged kidney cannot readily excrete the end products of protein metabolism, as measured by the nitrogen, and that a distinctly harmful result follows such a retention. The determination of a nitrogen balance in nephritis has been considered one of the valuable tests of the ability of the kidney to eliminate this substance. In the interpretation of this procedure, three factors have been considered essential :
An accurate determination of the food nitrogen.
An accurate determination of the output of the nitrogen in the urine and feces.
A constant intermediary nitrogenous metabolism. The first two of these demands are readily