URINE 407 



hydrogen phosphate, Na 2 HPO 4> that the greater part of the alkalinity 

 of the saliva is due. 



The excretion of phosphoric acid is extremely variable, but on the 

 average the total output for 24 hours is about 2.5 grams, expressed 

 as P20 5 . Ordinarily the total output is mainly in the form of phosphates 

 and is distributed between alkaline phosphates and earthy phosphates 

 approximately in the ratio 2:1. The organic phosphorus of the urine 

 constitutes only 1-4 per cent of the total phosphorus content. The 

 greater part of this phosphoric acid arises from the ingested food, either 

 from the preformed phosphates or more especially from the phosphorus 

 in organic combination such as we find it in phospho-proteins, nucleo- 

 proteins and lecithins; the phosphorus-containing tissues of the body 

 also contribute to the total output of this element. Alkaline phosphates 

 ingested with the food have a tendency to increase the phosphoric acid 

 content of the urine to a greater extent than the earthy phosphates so 

 ingested. This is due, in a measure, to the fact that a portion of the 

 earthy phosphates, under certain conditions, may be precipitated in the 

 intestine and excreted in the feces; this is especially to be noted in the 

 case of herbivorous animals. Since the extent to which the phosphates 

 are absorbed in the intestine depends upon the form in which they are 

 present in the food, under ordinary conditions, there can be no absolute 

 relationship between the urinary output of nitrogen and phosphorus. 

 If the diet is constant, however, from day to day, thus allowing of the 

 preparation of both a nitrogen and a phosphorus balance, 1 a definite 

 ratio may be established. In experiments upon dogs which were fed 

 an exclusive meat diet, the ratio of nitrogen to phosphorus, in the urine 

 and feces, was found to be 8.1 : i. 



It has been demonstrated by recent investigation that the ingestion of 

 inorganic phosphorus compounds may give rise to organic phosphorus 

 compounds such as lecithin, phosphatides, nucleoproteins and phospho- 

 proteins. This is an instance of an organic substance synthesized from 

 an inorganic substance. The experiments have been made principally 

 on'ducks 2 and hens. 3 



Pathologically the excretion of phosphoric acid is increased in such 

 diseases of the bones as diffuse periostosis, osteomalacia, and rickets; 

 according to some investigators, in the early stages of pulmonary tuber- 

 culosis, in acute yellow atrophy of the liver, in diseases which are ac- 

 companied by an extensive decomposition of nervous tissue, and after 



1 In metabolism experiments, a statement showing the relation existing between the 

 nitrogen content of the food on the one hand and that of the urine and feces on the other, 

 for a definite period, is termed a nitrogen balance or a "balance of the income and outgo of 

 nitrogen" (see chapter on Metabolism). 



2 Fingerling: Biochem. Zeit., 38, 448, 1912. 



3 McCollum and Halpin: Jour. Biol. Chem. t n, 47 (Proceedings), 1912. 



