EXAMINATION OF NORMAL AND ABNORMAL URINE. 461 



drop, when a deep-red color appears, if indigo-red is present. The 

 foam on shaking the test-tube is bluish-red. 



Odor. The normal odor of fresh urine is characteristic, and is 

 sometimes spoken of as aromatic; it is not known by what substance 

 or substances this odor is caused. The ammoniacal and putrescent 

 odor which urine acquires on standing is due to the products of de- 

 composition formed, chiefly ammonia. 



A number of substances taken internally and separated by the kidneys from 

 the blood, cause the urine to assume a characteristic odor ; aromatic substances 

 especially impart such odors; oil of turpentine gives an odor reminding of 

 violets, and the odor of cubebs, copaiba, asparagus, garlic, valerian, and other 

 substances is promptly transferred to the urine of persons using these drugs 

 internally. A sweetish smell sometimes attends the presence of large quantities 

 of sugar in urine. 



Reaction. This is generally acid in healthy urine which has been 

 recently passed, but may become neutral or alkaline within a short 

 period, by decomposition of urea and formation of ammonium car- 

 bonate. The acid reaction of urine is due chiefly to monosodium 

 ortho-phosphate, NaH 2 PO 4 , and perhaps also to the acid salts of 

 uric acid. 



The acidity may be determined volumetrically by the addition of deci-normal 

 solution of sodium or potassium hydroxide to 100 c.c. of urine, using litmus- 

 paper as an indicator. The acidity of urine is generally expressed as oxalic 

 acid, of which 1 c.c. of normal potash solution neutralizes 0.0063 gramme. If, 

 for instance, 100 c.c. of urine require 15 c.c. of deci-normal potash solution, 

 then the acidity of the 100 c.c. urine is 15 X 0.0063 = 0.0945 ; and for the total 

 urine of the 24 hours say 1800 c.c. the acidity expressed as oxalic acid is, 

 therefore, equal to 1.701 grammes. 



While urine shows an acid reaction generally, it may have a neutral 

 or even alkaline reaction. In many cases this alkaline reaction points 

 to decomposition of urea in the bladder, but it may be due also to the 

 elimination of alkali carbonates, derived from food taken or drugs 

 administered. 



Thus, the alkali tartrates, citrates, acetates, etc., have (after diges- 

 tion) a tendency to neutralize uric acid, and an excess of them is 

 eliminated as carbonate. 



To distinguish between the harmless alkaline reaction caused by 

 fixed alkalies and the alkaline reaction produced by decomposition of 

 urea, a piece of red litmus-paper may be used. If this, after having 

 been moistened with the urine, remains blue on drying (by warming 



