METABOLISM IN NEPHRITIS 



367 



The added urea and salt test gives us rather early evidence of disturbed 

 nitrogen and salt elimination of the kidney, as shown by delayed and 

 deficient excretion of these substances. Simple, logical and direct as it 

 seems, the test, has many practical difficulties. In the ten or twelve days 

 needed to carry it out the patient may tire of the hospital and refuse to 

 stay; changes in the patient's condition may necessitate a change in diet 

 or other interference with the conditions under which the experiment 

 is being carried out ; a woman may begin to menstruate ; portions of the 

 urine may be lost unavoidably as when the patient .voids at stool, etc. ; or 

 the diet may become very monotonous. Sometimes, especially during the 

 formation of edema, there may be a storing up of nitrogen or salt with 

 a subsequent discharge of the same either just before or coincidently with 

 the giving of the added urea or salt. This of course interferes with the 

 correct interpretation of the changes in the excretion curves. Urea taken 

 by mouth sometimes causes a diarrhea, with consequent probable loss of 

 an unknown amount of nitrogen in the feces. This would have the effect 

 of showing an apparently lower nitrogen excretion than the kidneys are 

 really capable of handling. Of course variations in rate and complete- 

 ness of absorption from the gastro-intestinal tract introduce possible errors 

 in such dietary tests. Tissue retention, especially of salt, is another pos- 

 sible source of error in any such test." 



It becomes clear from the above that there are many factors besides 

 the condition of the kidney which may influence the excretion of urea and 

 salt and that simply adding them to the food and determining the quan- 

 tity excreted may not yield the information desired concerning the kid- 

 ney function (see nitrogen balance in nephritis and tests for function of 

 the glomeruli and^ubules). It is comparatively simple theoretically to 

 judge of these tests when there is either an adequate elimination of the 

 added urea or salt or a straightforward retention of these substances (see 

 Table 25). 



TABLE 25 

 SALT EXCRETION TEST IN A NORMAL PERSON AND IN A CASE OF SECONDARY CONTRACTED 



KIDNEY; DELAYED EXCRETION OF SALT AND POLYURIA OCCURS IN THE NEPHRITIC 



PATIENT. (Munk) 



Some of the usual as well as the bizarre findings developed during the 

 course of these methods mav be cited : 



