XVI.] THE URINE. IO7 



Certain medicinal and other substances influence it — turpentine (violets) ; 

 cubebs, copaiba, and sandal -wood oil give a characteristic odour, and so do 

 asparagus, valerian, assafoetida, garlic, &c. In disease^ note the annnoniacal 

 odour of putrid urine and the so called "sweet" odour in saccharine 

 diabetes. 



7. Reaction. — Normal. — Slightly acid, it turns blue litmus- 

 paper slightly red, and does not affect red litmus-paper. 'J'lie 

 acidity is chiefly due to acid sodium phosphate (jN"aH2P04), acid 

 urates, and very slightly to free acids — lactic, acetic, oxalic, &c. 

 A neutral urine does not alter either blue or red litmus-paper. A 

 ve7y acid urine turns blue litmus-paper very red. 



(a.) Test with appropriate litmus-paper a normal, very acid, 

 neutral, and alkaline urine. 



(b.) Test also with violet litmus-paper. 



(c.) That the acidity is not due to a free acid is shown by its 

 giving no precipitate with sodium hyposulphite, and also by the 

 fact that it has no action on congo-red. The colour of the latter 

 body is violet or inky, with a solution containing i part of free 

 hippuric acid in 50,000 of distilled water. 



8. Variations in Acidity during the Day. — During digesUon, i.e., 

 two or three hours after a meal, the urine becomes neutral or alka- 

 line. The cause of the alkalinity, is a fixed alkali, probably derived 

 from the basic alkaline phosphates taken with the food {Roherls), 

 the ^^alkaline-tide." According to others, the formation of free 

 acid in the stomach liberates a corresponding amount of bases in 

 the blood, which pass into the urine, and diminish its acidity or 

 even render it alkaline. The " acid-tide " occurs after fasting. 



Nature of the Food. — With a vegetable diet the excess of alkali causes an 

 alkaline urine. In herbivora it is alkaline, in carnivora very acid. Herbivora 

 (rabbits) whilst fasting have a clear acid urine, because they are practically 

 living on their own tissues. Perhaps this is one of the reasons why the urine 

 is so acid in fevers. Inanition renders the urine renj acid {Chossal). In 

 herbivorous animals and vegetarians, the excess of alkaline salts of citric, 

 tartaric, and other acids being oxidised into carbonates render it alkaline. 



Medicines. — Acids slightly increase the acidity. Alkalies and their car- 

 bonates are more powerful than acids, and soon cause alkalinity ; alkalies, 

 e.g.^ the alkaline salts of citric, tartaric, malic, acetic, and lactic acids, appear 

 as carbonates ( Wohler). 



9. Alkalinity may be due to the Presence of a Fixed or a 

 Volatile Alkali. — In the former case, the blue colour of the litmus- 

 paper does not disappear on heating ; in the latter it does, and the 

 paper assumes its original red colour. 



{a.) Test with two pieces of red litmus-paper two samples of 

 urine, one alkahne from a fixed alkali, and the other from a vola- 

 tile one. Both papers become blue. 



