706 PHYSIOLOGICAL CHEMISTRY. 



homogentisic acid and uroleucic acid (alkapton) are excreted by the 

 kidneys. 



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 arnmoniacal 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. 



Volume. The amount of urine in twenty-four hours varies greatly 

 under physiological conditions. It is usually between 900 and 1500 c.c. 

 It is influenced very largely by the amount of water ingested, by 

 sweating, by diarrhoea, etc. It is decreased in acute nephritis, in- 

 creased in chronic nephritis, diabetes mellitus, and diabetes insipidus. 



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 and carbamate. The acid reaction of urine is due to mono- 

 sodium ortho-phosphate, NaH 2 PO 4 , and to free organic acids. These 

 organic acids have not as yet been identified. 



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 the urine, 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 

 gently) the reaction is due to the fixed alkalies ; if the red color 

 reappears, the alkaline is due to ammonia compounds. 



This distinction possesses no importance in urine which has become 

 alkaline on standing. 



