THE URINE. 81 



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

 acid, neutral, and alkaline urine. 



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



8. Variations during the Day. Two or three hours after a meal 

 the urine becomes neutral or alkaline. (See that the bladder be 

 emptied before beginning the experiment.) The cause of the 

 alkalinity is a fixed alkali, probably derived from the basic 

 alkaline phosphates taken with the food (Roberts). 



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 very acid (Chossat). 



Medicines. Acids slightly increase the acidity. Alkalies and 

 their carbonates 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 (Wb'hler). 



9. The 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 alkaline from a fixed alkali, and the other from 

 a volatile one. Both papers become blue. 



(6.) Place both side by side on a glass slide, heat them 

 carefully, and note that the blue colour of the one disappears 

 (volatile alkali), the red being restored, while the blue of the 

 other remains (fixed alkali). 



The alkalinity may be caused by the presence of ammonium 

 carbonate (volatile), derived from the decomposition of urea ; the 

 urine may be ammoniacal when passed, in which case there is 

 always disease of the urinary mucous membrane ; or it may 

 become so on standing from putrefaction when it is always 

 turbid, and contains a sediment consisting of amorphous phos- 

 phate of lime and triple-phosphate, and sometimes urate of 

 ammonium ; it has an offensive ammoniacal odour, and is very 

 irritating to the mucous membrane. 



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