URINE. 299 



Under these conditions, however, an examination of the blood of 

 the fasting subject will show the percentage of chlorides in this 

 fluid to be approximately normal. This forms a very striking ex- 

 ample of the care nature takes to maintain the normal composition 

 of the blood. There is a limit to the power of the body to main- 

 tain this equilibrium, however, and if the fasting organism be sub- 

 jected to the influence of diuretics for a time, a point is reached 

 where the composition of the blood can no longer be maintained and 

 a gradual decrease in its chloride content occurs which finally re- 

 sults in death. Death is supposed to result not so much because of 

 a lack of chlorine as from a deficiency of sodium. This is shown 

 from the fact that potassium chloride, for instance, cannot replace 

 the sodium chloride of the blood when the latter is decreased in the 

 manner above stated. When this substitution is attempted the 

 potassium salt is excreted at once in the urine, and death follows as 

 above indicated. 



Pathologically, the excretion of chlorides may be decreased in 

 some fevers, chronic nephritis, croupous pneumonia, diarrhoea, cer- 

 tain stomach disorders and in acute articular rheumatism. 



EXPERIMENT. 



Detection of Chlorides in Urine. Place about 5 c.c. of urine in 

 a test-tube, render it acid with nitric acid and add a few drops of a 

 solution of argentic nitrate. A white precipitate, due to the forma- 

 tion of argentic chloride, is produced. This precipitate is soluble 

 in ammonium hydroxide. 



Phosphates. 



Phosphoric acid exists in the urine in two general forms : First, 

 that in combination with the alkali metals, sodium and potassium, 

 and the radical ammonium; second, that in combination with the 

 alkaline earths, calcium and magnesium. Phosphates formed 

 through a union of phosphoric acid with the alkali metals are termed 

 alkaline phosphates, or phosphates of the alkali metals, whereas 

 phosphates, formed through a union of phosphoric acid with the 

 alkaline earths are termed earthy phosphates, or phosphates of the 

 alkaline earths. 



Three series of salts are formed by phosphoric acid : Normal, 

 MgPC^, 1 mono-hydrogen, M 2 HPO 4 , and di-hydrogen, MH 2 PO 4 . 

 The di-hydrogen salts are acid in reaction and it was generally be- 

 lieved that about 60 per cent of the total phosphate content of the 



1 M may be occupied by any of the alkali metals or alkaline earths. 



