1164 PHYSIOLOGY 



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 (P0 4 ) 2 . 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 

 crystalline precipitate of ammonium magnesium phosphate, NH 4 MgP0 4 , 

 the so-called ' triple phosphate.' 



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

 ammonia, magnesia, and lime. 



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 0*2 grm. Their output by the urine is no criterion of 

 the amount taken in with the food or absorbed from the intestines, since 

 both these bases may be re -excreted into the gut and appear as insoluble 

 phosphates in the faeces. 



Normal human urine always contains a small amount of ammonia, on 

 an average between 0-6 and O8 grm. in the twenty-four hours. As we 

 have already seen, in dealing with the origin of urea in the body, the quantity 

 of ammonia in the urine is an index to the excess of acids over bases which 

 have to be excreted by this fluid. Thus it is easily possible to increase the 

 proportional amount of ammonia in the urine by the administration of 

 mineral acids. An increase of the proportion of nitrogen excreted as 

 ammonia, apart from the administration of acids with the food, is an 

 important indication of the formation of abnormal acid substances in meta- 

 bolism. Thus in diabetes, when the last stages of fat oxidation are in 

 default, so that the oxy-fatty acids, /?-oxybutyric and aceto-acetic acids, 

 accumulate in the body, there is always a considerable rise in the ammonia 

 of the urino. 



It is usual to reckon iron among the bases which may be excreted by the 

 urine. The amount of this substance in the urine is extremely small, as a 

 rule less than 5 mg. in the day. It affords no clue to the iron metabolism 

 of the body, since the main channel of excretion of this substance is the 

 intestine. 



