1244 PHYSIOLOGY 



and magnesium, the amount of phosphates excreted by the urine 

 diminishes, since these substances are excreted with the faeces as 

 calcium and magnesium phosphates. According to the diet therefore, 

 phosphoric acid may be excreted either by the intestine or by the 

 kidneys. The amount of phosphates, reckoned as P 2 5 , excreted 

 in the course of the day may vary between 1 and 5 grm. In the urine 

 the phosphates exist as a mixture of the mono- and di-sodium 

 phosphates, the relative amounts of the two varying with the 

 acidity of the urine. If the urine is neutral or alkaline there is 

 very often a deposit of earthy phosphates. Whether this deposit 

 is present or not depends on the varying solubility of the different 

 calcium and magnesium phosphates. Thus the mono-magnesium 

 phosphate MgH 4 (P0 4 ) 2 and the mono-calcium phosphate CaH 4 (P0 4 ) 2 

 are both fairly soluble in water, and their solubility is increased by 

 the presence of neutral salts. With increased acidity of the urine the 

 proportion of the two bases present in these forms is diminished. The 

 di-magnesium and di-calcium phosphates are only slightly soluble in 

 water, and the latter would, if present in the urine, be deposited. 

 One may indeed, in slightly acid urine, find the di-calcium phosphate 

 occasionally present as a crystalline deposit. On heating the urine 

 the di-calcium phosphate breaks up into a mono-calcium phosphate 

 and a tri-calcium phosphate, while the acidity of the urine is increased 

 by the solution of the mono-calcium phosphate. Alkaline urine will 

 always present a precipitate of tri-calcium phosphate Ca 3 (P 2 4 ) 8 . 

 When normal urine is allowed to stand, the urea is converted by the 

 presence of micro-organisms into ammonium carbonate, and the urine 

 becomes alkaline. Under such conditions we may often find a crystal- 

 line precipitate of ammonium magnesium phosphate, NH 4 MgP0 4 , the 

 so-called ' triple phosphate.' 



(6) THE BASES OF THE URINE. The bases include potassium, 

 sodium, ammonium, magnesium, and calcium. 



The amount of potash excreted in twenty-four hours varies between 

 1/9 and 3 - 2 grm., according to the nature of the food taken. With a 

 large meat diet, which contains considerable quantities of potassium, 

 the output of this base is increased. In fasting there is also an increase 

 in the output of potash, owing to the utilisation of the tissues of the 

 body which themselves are rich in potassium. 



The amount of sodium excreted in the twenty-four hours varies 

 on the average between 4 and 5 grm., but depends very largely on the 

 quantity of sodium chloride taken with the diet. The alkaline earths, 

 lime and magnesia, are invariably present in urine, but in much 

 smaller quantities than the alkaline metals. The average amount of 

 these two bases in the twenty-four hours varies in each case between 

 0- 1 and O2 grm. Their output by the urine is no criterion of the amount 



