394 A MANUAL OF PHYSIOLOGY 



Water. A marked and persistent diminution in the 

 quantity of urine, that is to say, practically in the water, with 

 or without an increase in the specific gravity, is suggestive 

 of disorganization of the renal epithelium. In some infective 

 diseases the kidney is liable to be secondarily involved, its 

 secreting cells being perhaps crippled in the attempt to 

 eliminate the bacterial poisons. In the form of parenchy- 

 matous or tubal nephritis which so frequently complicates 

 scarlet fever, the quantity of urine has in some cases fallen 

 to 50 or 60 c.c. in the twenty-four hours. 



In interstitial nephritis, on the other hand, where the 

 structural changes in the tubules are for a long time at least 

 comparatively circumscribed, the quantity of urine is often 

 increased, seldom diminished. In these cases the increase 

 in the blood-pressure, associated with hypertrophy of the 

 heart, may be considered responsible for the exaggerated 

 renal secretion. In diabetes mellitus the quantity of urine 

 is greatly increased, perhaps in some cases because more 

 urea is excreted than normal and urea acts as a diuretic, 

 perhaps also because the elimination of sugar draws with 

 it an increased excretion of water to hold it in solution. 

 Although a specific gravity as low as 1002 has been seen 

 in healthy persons (after copious potations), the persistence 

 of a density below 1010 should suggest hydruria. On the 

 other hand, while the specific gravity has been occasionally 

 observed to mount in health to at least 1036, its persistence 

 at 1025 to 1030 or anything above this, especially if the 

 urine is pale and apparently dilute, should suggest diabetes 

 mellitus. 



Inorganic Salts. The changes in the quantity of the in- 

 organic constituents of the urine in disease are not, in the 

 present state of our knowledge, of as much importance as 

 the changes in the organic constituents. The chlorides may 

 totally disappear from the urine in pneumonia, and their 

 reappearance after the crisis is, so far as it goes, a favour- 

 able symptom. In most cases in which the quantity of the 

 urine is markedly lessened, all the inorganic substances are 

 diminished in amount. 



Urea. The quantity of urea is, as a rule, increased in 



