REACTIONS OF THE URIXE. 353 



urinary bladder. When first discharged it is not visible, owing to 

 its being uniformly disseminated through the urine by mechanical 

 agitation ; but if the fluid be allowed to remain at rest for some 

 hours in a cylindrical glass vessel, the mucus collects at the bottom, 

 and may then be seen as a light cottony cloud, interspersed often 

 with minute semi-opaque points. It plays, as we shall hereafter 

 see, a very important part in the subsequent fermentation and 

 decomposition of the urine. 



Biphosphate of soda exists in the urine by direct solution, since it is 

 readily soluble in water. It is this salt which gives to the urine its 

 acid reaction, as there is no free acid present, in the recent condition. 

 It is probably derived from the neutral phosphate of soda in the 

 blood which is decomposed by the uric acid at the time of its form- 

 ation ; producing, on the one hand, a urate of soda, and converting 

 a part of the neutral phosphate of soda into the acid biphosphate. 



The phosphates of lime and magnesia, or the " earthy phosphates,'' 

 as they are called, exist in the urine by indirect solution. Though 

 insoluble, or very nearly so, in pure water, they are held in solu- 

 tion in the urine by the acid phosphate of soda, above described. 

 They are derived from the blood, in which they exist in considera- 

 ble quantity. When the urine is alkaline, these phosphates are 

 deposited as a light-colored precipitate, and thus communicate a 

 turbid appearance to the fluid. When the urine is neutral, they 

 may still be held in solution, to some extent, by the chloride of 

 sodium, which has the property of dissolving a small quantity of 

 phosphate of lime. 



The remaining ingredients, phosphates of soda and potassa, sul- 

 phates and chlorides, are all derived from the blood, and are held 

 directly in solution by the water of the urine. 



The urine, constituted by the above ingredients, forms, as we 

 have already described, a clear amber-colored fluid, with a reaction 

 for the most part distinctly acid, sometimes neutral, and occasion- 

 ally slightly alkaline. In its healthy condition it is affected by 

 chemical and physical reagents in the following manner. 



Boiling the urine does not produce any visible change, provided 

 its reaction be acid. If it be neutral or alkaline, and if, at the same 

 time, it contain a larger quantity than usual of the earthy phos- 

 phates, it will become turbid on boiling ; since these salts are less 

 soluble at a high than at a low temperature. 



The addition of nitric or other mineral acid produces at first onl v 

 23 



