METABOLISM IN NEPHRITIS 



379 



Criterion 



Maximal specific 

 gravity. 



Normal 

 Standard. 



1920 + 



Significance. 



Fixation specific 

 gravity. 



Variation of 

 9 degrees 



Ability of the kidney to concentrate 

 the urine. If this is as high or higher 

 than the normal standard, renal ex- 

 cretion is satisfactory provided the 

 amount of urine is adequate. This 

 may be regarded as a definite cri- 

 terion of renal function which is 

 independent of the diet administered. 

 Long life is often possible even if the 

 specific gravity is below normal, pro- 

 vided the inability of the kidney to 

 concentrate is compensated by poly- 

 uria, as in diabetes insipidus and a 

 few cases of chronic nephritis. 

 Normal renal activity is character- 

 ized by variation of the specific grav- 

 ity in the urinary specimens. 



(a) A high fixed specific gravity may 

 occur in normal individuals because 

 they take too little fluid to meet their 

 bodily needs. The possibility of de- 

 termining this makes the two-hour 

 test especially valuable in ambulant 

 patients who are taking their usual 

 amount of food and fluid and are pur- 

 suing their accustomed occupations. 



(b) A high fixed specific gravity may 

 be brought about by diseases charac- 

 terized by edema and oliguria, es- 

 pecially myocardial insufficiency and 

 acute or chronic nephritis. 



(c) A low fixed specific gravity is 

 found in many widely varying condi- 

 tions: diabetes insipidus, chronic 

 nephritis, marked anemia, the elimi- 

 nation of edema, cystitis, pyelitis, 

 polycystic kidney, prostatic hyper- 

 trophy, urethral stricture, paralysis 

 of the bladder (as in tabes dorsalis 

 or tumor of the cord), etc. Such pa- 

 tients do well as long as polyuria com- 



