3OO PHYSIOLOGICAL CHEMISTRY. 



urine was in the form of this type of salt, and that the acidity of 

 the urine was due in great part to the presence of sodium di-hydro- 

 gen phosphate. Recently, however, it has been quite clearly shown 

 that the normal acidity of the urine is not due to the presence of this 

 salt but is due, at least in part, to the presence of various acidic 

 radicals. In this connection Folin believes that the phosphates in 

 clear acid urine are all of the mono-hydrogen type, and that the 

 acidity of the urines of this character is generally greater than 

 the combined acidity of all the phosphates present; the excess in 

 the acidity above that due to phosphates he believes to be due to 

 free organic acids. The observation has recently been made that 

 urine may be separated into two portions, one part consisting al- 

 most entirely of inorganic matter including practically all of the 

 phosphates and having an alkaline reaction, the other containing 

 practically all of the organic substances and no phosphates and hav- 

 ing an acid reaction. 



In bones the phosphates occur principally in the form of the nor- 

 mal salts of calcium and magnesium. The mono-hydrogen salts as 

 a class are alkaline in reaction to litmus, and it is to the presence of 

 di-sodium 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, ex- 

 pressed as P 2 O 5 . Ordinarily the total output is distributed be- 

 tween alkaline phosphates and earthy phosphates approximately in 

 the ratio 2:1. 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, nude o proteins and lecithins; the phos- 

 phorus-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, 



