INORGANIC CONSTITUENTS OF THE URINE 349 



It is a question of some importance to consider how far the phos- 

 phates are derived from the tissues and what proportion comes directly 

 from food. All observers agree that the quantity of phosphates in the 

 urine is in direct relation to the proportion in food, and that an excess 

 of phosphates taken into the stomach is immediately thrown off by the 

 kidneys. It is a familiar fact, indeed, that the phosphates are deficient 

 and the carbonates predominate in the urine of the herbivora, while the 

 reverse obtains in the carnivora, and that variations, in this respect, in 

 the urine may be produced by feeding animals with different kinds of 

 food. Deprivation of food diminishes the quantity of phosphates in the 

 urine, but a certain proportion is discharged that is derived exclusively 

 from the tissues. 



In connection with the fact that phosphorus exists in considerable 

 quantity in the nervous matter, it has been assumed that mental exer- 

 tion is attended with an increase in the elimination of phosphates ; and 

 this has been advanced to support the view that these salts are. specially 

 derived from katabolism of the brain-substance. Experiments show 

 that it is not alone the phosphates that are increased in quantity by 

 mental work, but urea, the chlorides, sulphates and inorganic matters 

 generally ; and in point of fact, physiological conditions that increase 

 the proportion of nitrogenous excrementitious matters increase as well 

 the elimination of inorganic salts. It can not be assumed, therefore, 

 that the discharge of phosphates is specially connected with the activity 

 of the brain. Little has been learned on this point from pathology ; for 

 although many observations have been made on the excretion of phos- 

 phoric acid in disease Vogel having made about one thousand dif- 

 ferent analyses in various affections no definite results have been 

 obtained. From these facts it is seen that there is no physiological 

 reason why the elimination of the phosphates should be specially con- 

 nected with the katabolism of any particular tissue or organ, espe- 

 cially as these salts in some form are universally distributed in the 

 organism. 



Observations have been made on the hourly variations in the dis- 

 charge of phosphoric acid at different times of the day; but these do 

 not appear to bear any definite relation to known physiological condi- 

 tions, not even to the process of digestion. 



Of the different phosphatic salts of the urine, the most important 

 are those in which the acid is combined with sodium. These exist in 

 the form of the neutral and acid phosphates. The acid salt is sup- 

 posed to be the source of the acidity of the urine at the moment of 

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

 portion of the sodium phosphates in the urine is larger than that of any 



