278 APPLIED PHYSIOLOGY 



The percentage acidity of the day urine is also reduced 

 by the ' alkaline tide ' which follows meals, and which 

 is due to the alkaline carbonates set free in the blood as 

 the result of the elaboration of the gastric juice. 



By estimating the total acidity of the urine and that 

 part of it which is due to phosphoric acid separately, 

 one can arrive at a measure of the amount of the 

 acidity which is due to the presence of unoxidized 

 organic acids, and which are often an index of some 

 disorder of metabolism. A method of doing this has 

 been devised by M. Joulie, and has been largely 

 employed in clinical work in France. 



Nitrogenous Constituents. 



Of the total amount of nitrogen (about 16 grammes) 

 excreted in the urine on an ordinary diet 



84 to 87 per cent, is in the form of urea ; 

 2 to 5 per cent, is in the form of ammonia 



compounds ; 

 1 to 3 per cent, is in the form of uric acid ; 



whilst the balance is contained in such substances as 

 purin bases, hippuric acid, creatinin, and some undeter- 

 mined compounds. 



Urea. The amount of urea present in the urine 

 depends almost entirely upon the amount of protein in 

 the food. It is therefore useless to estimate it for 

 clinical purposes unless the composition of the diet is 

 taken into consideration. Seeing that it is mainly 

 formed in the liver from ammonia compounds, it is 



