EXCKETIONS 483 



in warm weather the volume may be as low as 350 c.c., while a volume of 

 1500 to 1800 c.c. may be encountered during cold weather. 



The condition of the cardiovascular system and kidneys has much to 

 do with the volume of urine eliminated. In interstitial nephritis, the 

 volume of urine is usually large, frequently 2000 c.c. .or over. Of par- 

 ticular interest is the observation that in this condition an abnormallv 

 large volume of dilute urine is eliminated during the hours from 8 P.M. to 

 8 A.M. This night polyuria commonly results in an elimination con- 

 siderably in excess of 400 c.c., the usual output during these hours. In 

 parenchymatous nephritis, the relations are not so constant, but in general 

 the urine is concentrated and the volume reduced. The variations in 

 volume in such cases are usually referable to the formation or disap- 

 pearance of edema. A very large volume of dilute urine (5000 c.c. or 

 more) may be eliminated in diabetes insipidus, due probably to dilatation 

 of the renal vessels. The 'volume is increased when it is necessary to 

 eliminate a large amount of material, as is the case with sugar in diabetes 

 mellitus. A temporarily increased output of urine may result through 

 nervous influences. 



Color. The color of urine may vary under normal conditions from a 

 very pale yellow to a reddish yellow or deep amber, depending upon its 

 density. The color is due principally to a pigment called urochrome, 

 although small amounts of urobilin, and occasionally traces of uroerythrin 

 may be present. Pathologically the color may vary from a perfectly 

 colorless fluid to dark brown or black. A red color may be due to blood, 

 occasionally to hematoporphyrin ; very dark colored urines may arise 

 from taking carbolic acid ; the excretion of melanin from pigmented 

 tumors may likewise be the cause of a dark color, especially after being 

 exposed to the air for some time or on the addition of an oxidizing agent. 

 A green or brownish yellow color may be due to bile, also recognized by 

 the yellow tinged foam. In alkaptonuria the urine may become dark 

 owing to the presence of homogentisic acid. This is especially so if the 

 urine is allowed to become alkaline. 



Specific Gravity. The specific gravity of normal urine most commonly 

 falls between 1.015 and 1.025. It may, however, be as low as 1.008 or as 

 high as 1.040 without necessarily indicating pathological conditions. Nor- 

 mally the specific gravity is inversely proportional to the volume. In 

 diabetes mellitus one may observe both a large volume and a high specific 

 gravity owing to the presence of sugar. In interstitial nephritis the 

 specific gravity is persistently low and fixed regardless of variations in 

 volume. 



Odor. Normal urine has a faint but characteristic aromatic odor. As 

 urine undergoes alkaline fermentation, a disagreeable ammoniacal odor 

 develops. 



Reaction and Acidity. The principal factor involved in the regula- 



