330 FUNCTIONS OF NUTRITION. 



urine its acid reaction. It is regarded as derived from the sodium 

 phosphate of the blood (Na 2 H P0 4 ) by the action of uric acid, which 

 unites with a part of its sodium, forming sodium urate, and leaving an 

 acid sodium phosphate (NaH 2 P0 4 ). The uric acid produced in the 

 system, though not eliminated in a free form, causes, therefore, indi- 

 rectly the acid reaction of the urine ; and this reaction will vary in 

 intensity with the amount of its production. 



The Alkaline Phosphates, or phosphates of sodium and potassium. 

 These phosphates exist in the blood as well as in the urine, and in 

 solution have a mildly alkaline reaction. Owing to their ready solu- 

 bility, they never appear as a precipitate, nor disturb in any way the 

 transparency of the urine. It is as a constituent of these salts that 

 most of the phosphoric acid in combination is discharged with the urine. 

 According to Yogel, its excretion is increased by food containing sol- 

 uble phosphates or substances capable of yielding phosphoric acid in 

 the system. It is accordingly more abundant under a diet of animal 

 food, less so under a vegetable regimen. It is not, however, exclu- 

 sively derived from the food, since it is still discharged, though in dimin- 

 ished quantity, after long-continued abstinence. Its immediate origin 

 is, therefore, wholly or partly from the constituents of the body itself. 

 The observations of Wood,* as well as those of Yogel, show a diurnal 

 variation of considerable regularity in the excretion of the phosphatic 

 salts. It is at a minimum during the forenoon, increases in the latter 

 part of the day after the principal meal, and reaches a maximum in the 

 evening or during the night, to diminish again on the morning of the 

 following day. The average quantity of the alkaline phosphates dis- 

 charged under an ordinary diet is a little over four grammes per day. 



The Earthy Phosphates, or phosphates of lime and magnesia. The 

 earthy phosphates are usually excreted in much smaller quantity than 

 the preceding. They arc held in solution by the acid reaction of the 

 urine, and when this reaction is absent or much diminished they are 

 thrown down as a light precipitate. The neutral or faintly alkaline 

 urine, often passed in the forenoon, may therefore be turbid with a 

 deposit of earthy phosphates, without indicating any abnormal increase 

 in their amount. According to the observations of Wood, the alkaline 

 and earthy phosphates differ in the conditions influencing their excre- 

 tion. During continued mental application, the alkaline phosphates are 

 increased, while the earthy phosphates are diminished ; the amount of 

 both combined being not materially altered. The average daily quan- 

 tity of the earthy phosphates is about one gramme, or rather less than 

 one-quarter that of the alkaline phosphates. 



Sodium and Potassium Chlorides. Sodium chloride, which rep- 

 resents nearly the whole of these salts, is by far the most abundant 

 mineral ingredient in the urine, forming over one-half of its inorganic 

 constituents. It is mainly derived from the food, and is increased 



* Proceedings of the Connecticut Medical Society, 1869. 



