21 6 EXCRETION. 



Observations have been made upon the hourly variations 

 in the discharge of phosphoric acid at different periods of the 

 day ; but these do not appear to bear any absolute relation 

 to known physiological conditions, not even to the process 

 of digestion. 1 



Of the different phosphatic salts of the urine, the most 

 important are those in, which the acid is combined with soda. 

 These exist in the form of the neutral and acid phosphates. 

 The acid salt has one equivalent of the base, and is supposed 

 to be the cause of the acidity of the urine at the moment of 

 its emission. The so-called neutral salt is slightly alkaline, 

 and has two equivalents of base. The proportion of the 

 phosphates of soda in the urine is larger than that of any of 

 the other phosphatic salts, but the daily amount excreted has 

 not been estimated. The phosphate of magnesia is a constant 

 constituent of the urine, as well as the acid and the basic phos- 

 phate of lime. The daily excretion of phosphate of magne- 

 sia amounts to from 7 *T to 11*8 grains, and of the phosphates 

 of lime, from 4'Y to 5*7 grains. 2 According to Robin, there 

 always exists in the urine a small quantity of the ammonio- 

 magnesian phosphate, but it never, in health, exists in suffi- 

 cient quantity to form a crystalline deposit. 8 The daily 

 excretion of the phosphates is, as we have seen, subject to 

 great variations, but the average quantity of phosphoric acid 

 excreted daily may be estimated at about fifty grains, or, 

 more accurately, fifty-six grains. 4 



The urine contains, in addition to the inorganic prin- 

 ciples above described, a small quantity of silicic acid ; 

 but, as far as we know, this has no physiological im- 

 portance. 



1 The reader is referred to the work of Neubauer and Vogel for a fuller 

 consideration of the physiological and pathological relations of the phos- 

 phates. 



2 NEUBAUER AND VOGEL, op. cit., p. 59. 



3 ROBIN, Lemons sur les humeurs, Paris, 1867, p. 6"66. 



4 THUDICHUM, A Treatise on the Pathology of the Urine, London, 1858, p. 

 416. 



