METABOLISM IN NEPHKITIS 333 



not usually occur either in the blood or tissues, even when there is marked 

 renal insufficiency as shown by the increase in the urea content. Woods 

 obtained similar analyses, excepting a case suffering with complete anuria 

 for 5 days, in which the ammo acid nitrogen reached a level of 16.32 mg. 

 It is to be expected that the amino acids in the blood and tissues should 

 remain at a normal level, inasmuch as, if those acids ordinarily destined 

 to be excreted in the urine are retained because of renal insufficiency, the 

 liver would transform them to urea, and they would thus lose their chem- 

 ical identity. It seems probable, therefore, that the amino acid content 

 of the blood and muscles remains normal in nearly all cases of nephritis. 

 The few cases reported in which the amino acid nitrogen in the blood is 

 increased remain to be confirmed. It is possible that the liver can not 

 deaminize certain amino acids very readily and if these occur in larger 

 amounts than usual, they may accumulate in the blood and tissues if the 

 kidney is unable to eliminate them. 



The Nitrogen Balance in Nephritis 



Before the advent of blood chemistry, the determination of the nitro- 

 gen balance in nephritis was regarded as one of the most reliable tests 

 of the ability of the kidney to eliminate this substance. This in a meas- 

 ure is still true, though there are certain conditions that limit the value 

 of this procedure. For the proper interpretation of a nitrogen balance, 

 three factors must be known : 



1. The nitrogen intake. 



2. The nitrogen output in the urine and feces. 



3. The course of intermediary nitrogenous metabolism. 



The first two of these demands are readily fulfilled; the third is vague 

 in its requirements and no definite standards can be established for it ; 

 consequently much must be left to the judgment of the clinician or in- 

 vestigator. However, by the proper application of the figures for non- 

 protein nitrogen or urea in the blood, many of the facts that were formerly 

 left to chance may be accorded their true meaning. 



Besides the simple equation between intake and output, there are some 

 processes that may cause a discrepancy in the nitrogen balance which 

 makes it somewhat difficult to be certain of the actual meaning of this 

 procedure. The tendency has been to attribute a lag of nitrogen elimina- 

 tion to renal insufficiency in every instance; however, if the tissues in- 

 corporate the ingested nitrogen, that is, assimilate it, a positive nitrogen 

 balance results which may be due to physiological processes and not to 

 pathological changes in the kidney (see Table 17). An augmented pro- 

 tein destruction or a marked loss of water mav serve to raise the level 



