484 VICTOK C. MYEES 



tion of urinary acidity is the proportion between the acid sodium 

 phosphate (H 2 XaPO 4 ) and the basic sodium phosphate (HNa 2 PO 4 ), the 

 former raising the acidity and the latter lowering it. The principal acid 

 supply is found in the metabolism of protein, during which sulphuric acid 

 is formed from the oxidation of the sulphur of the protein, while phos- 

 phoric acid is set free. The organic acids, uric, hippuric, oxalic, and 

 certain of the lower fatty acids also contribute to the acidity. The basic 

 radicals concerned are sodium, potassium, ammonium, calcium and mag- 

 nesium. The excretory function of the kidney normally prevents any 

 undue accumulation of either acids or bases in the body, thereby main- 

 taining a remarkable constancy in the reaction of the body fluids. 



Urine is most commonly acid to litmus. The reaction and degree of 

 acidity may, however, experience marked change under both physiological 

 and pathological conditions. The diet is one of the most important factors 

 involved. In general, the metabolism of animal foods, except milk, results 

 in an increased acidity, while vegetable foods, except the cereal grains, 

 tend to diminish the acidity or even yield alkaline urines. The reason 

 for this general difference between animal and vegetable food materials is 

 due, as pointed out by Sherman and Gettler, to their excess of acid- or base- 

 forming elements. These considerations probably account for the fact 

 that the urine of dogs is normally acid, while that of rabbits is habitually 

 alkaline. 



The pathological formation of acids (as in diabetes) is counteracted 

 in a measure by the neutralizing action of the bases, sodium, potassium, 

 calcium and magnesium. When the acidity .is so great that an adequate 

 supply of these elements can no longer be economically furnished by the 

 body, ammonia is called upon to meet this need. This accounts for the 

 increased elimination of ammonia in diabetic ketosis. The proximity to a 

 meal may affect the reaction of the urine. For example, the secretion of 

 hydrochloric acid in the stomach during the process of digestion may so 

 reduce the store of acids in the body that for a time after a meal the 

 urine may be neutral or even alkaline, giving rise to the so-called "alka- 

 line tide." 



Quantitative expression may be given to the acidity of the urine by 

 determining the number of cubic centimeters of tenth normal sodium 

 hydroxid required to neutralize the total volume of urine eliminated in 

 24 hrs. This represents the titratable acidity, and may range from 200 

 to 500, with an average of about 350. 



The titratable acidity should be distinguished from the true acidity, 

 the latter depending upon the concentration of ionized hydrogen (H+). 

 From this point of view, a solution is acid, neutral or alkaline, depending 

 upon the relative concentrations of hydrogen ions (H 4 ) and of l^droxyl 

 ions (OH"). An acid solution therefore contains a greater concentration 

 of (H*) than of (OH"), For convenience in recording the hydrogen ion 



