URINE. 



Considered from the physiological point of view, the 

 urine forms the chief exit for those soluble substances which, 

 either on account of their toxicity under certain conditions 

 or from their lack of available potential energy, are unsuited 

 for utilization and further retention in the organism. Chem- 

 ically, the urine presents a watery solution of organic and 

 inorganic bases and acids, whose degree and manner of com- 

 bination is dependent upon the conditions (affinity, mass- 

 action, etc.) existent in the solution. The compounds 

 present in the urine represent, on the one hand, the end 

 products of combustion and cellular metabolism, and, on 

 the other, bodies excreted in the same or similar form in 

 which they were ingested. It is this double origin of the 

 constituents of the urine which necessitates a comprehensive 

 knowledge of the daily ingesta, if rational or accurate de- 

 ductions are to be made from the composition of the urine. 

 Again, as the character and composition of the urine ex- 

 creted at different periods of the day varies within rather 

 wide limits, it is absolutely essential in every examination 

 of urine that the sample presented for analysis should repre- 

 sent a definite part, if not the whole, of a well-mixed 24-hours 

 excretion. This in part affords an explanation of the now 

 current method of considering the constituents of the urine 

 from the standpoint of weight per diem (grammes) rather than 

 concentration (per cent). Percentage data neglect one 



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