158 PHYSIOLOGICAL CHEMISTRY 



add just the right amount of acid, as excess or a deficient amount 

 will result in incomplete precipitation of the protein. 



Consistency, Odor, Taste. The urine usually is thin and 

 watery. It foams on shaking but the foam quickly disappears. 

 If the urine is albuminous the foam may persist. If it contains 

 much mucin or pus, the urine may be thickish in character. 



The odor of fresh urine somewhat resembles that of a meat 

 broth. It is quite characteristic. Little is known of the nature 

 of the substances responsible for the odor. Recently a substance 

 "urinod" has been reported. When urine is allowed to stand 

 without a preservative, it quickly acquires a sharp ammoniacal 

 odor. Decomposition has taken place. With a little practice, 

 the analyst is able to detect when a urine has ' ' spoiled, ' ' and be- 

 come unsuitable for analysis. Albumin or pus urine, especially 

 if old, often has a putrid odor. Ingested drugs or foods may 

 cause an unusual odor, thus asparagus, or onions give the urine 

 a disagreeable odor. After taking menthol, an odor of pepper- 

 mint is observed. 



The taste of normal urine usually is somewhat salty due to 

 NaCl. Diabetic urine may taste sweet, from the sugar present. 



Specific Gravity. Total Solids. The specific gravity of nor- 

 mal urine obviously depends upon the relation between the 

 amount of total solids, and the volume of the urine. An average 

 specimen will have a specific gravity of from 1.017-1.020, but it 

 may fall to 1.010 or lower if the volume is large, or rise to 1.030 

 or higher if the volume is low or the total solids high. In new 

 born infants the specific gravity is low, about 1D05-1.007. 



In pathological conditions the volume and specific gravity 

 may not vary inversely. Thus in diabetes mellitus a large vol- 

 ume is accompanied by a fairly high specific gravity, on account 

 of the sugar present. In cases of albuminuria the volume may 

 be low and the specific gravity low also. 



Specific gravity usually is estimated by means of an areom- 

 eter or urinometer. (See laboratory directions for urine.) 



The total solids excreted in the course of a day will vary 

 considerably. Sixty grams is an average figure. The amount de- 



