I08 PRACTICAL PHYSIOLOGY. [XVI 



(b.) 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 ammonia- 

 cal 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 phosphate of 

 lime and triple-phosphate, and sometimes urate of ammonium ; it has an 

 otlensive ammoniacal odour, and is very irritating to the mucous membrane. 



The acidity is increased during the resolution of febrile diseases ; is excessive 

 in gout and acute rheumatism, and whenever much uric acid is given off (uric 

 acid diathesis) ; in saccharine diabetes ; when certain acids are taken with the 

 food (COo, benzoic). 



The amount of the acidity may be determined by using a standard solution 

 of caustic soda (p. i lo). 



f-— * 



YiQ. 53.— Deposit in " Acid Fermentation " of Urine, a. Fungus ; 6. Amorphous 

 sodium urate ; c. Uric acid ; d. Calcium oxalate. 



10. Transparency. — Observe whether the urine' is quite trans- 

 parent or contains any suspended particles, rendering it more or 

 less turbid, either when it is passed, or some time afterwards. 



11. Fermentation of Urine. — When urine is freely exposed to 

 the air it undergoes two fermentations — (i) the acid; (2) the 

 alkalme. The urine at first becomes slightly inore acid, from the 

 formation of lactic and acetic acids (although this is denied by some 

 observers), then it gradually becomes neutral, and finally alkaline 

 from putrefaction. It becomes lighter in colour, turbid, and a 

 whitish heavy precipitate occurs ; a pellicle forms on the surface, it 



