CHAP, iv.] RENAL SECRETION. 395 



proteolytic, from which it appears probable that some of the 

 ferments of the salivary glands, pancreas, stomach, &c., having done 

 their work, escape from the body by the urine. 



7. Gases. Those gases which can be extracted from urine by 

 the mercurial pump are chiefly nitrogen and carbonic acid, oxygen 

 occurring in very small quantities or being wholly absent. 

 , The quantities in which these multifarious constituents are pre- 

 sent vary within very wide limits, being dependent on the nature 

 of the food taken, and on the conditions of the body. These 

 points will be considered in the succeeding chapter. What may be 

 called the average composition of human urine is shewn in the fol- 

 lowing table. 



AMOUNTS OF THE SEVERAL URINARY CONSTITUENTS PASSED IN 

 TWENTY-FOUR HOURS. (After PAEKES.) 



By an average Per 1 kilo 



man of 66 kilos. of Body Weight. 



Water 1500*000 grammes 23*0000 grammes 



Total Solids 72-000 1*1000 



Urea 33*180 '5000 



Uric Acid '555 '0084 



Hippuric Acid '400 '0060 



Rreatinin '910 '0140 

 Pigment, and 



other substances lO'OOO '1510 



Sulphuric Acid 2'012 '0305 



Phosphoric Acid 3*164 '0480 



Chlorine 7*000 (8'21) '1260 



Ammonia '770 



Potassium 2*500 



Sodium 11-090 



Calcium -260 



Magnesium "207 



Acidity of Urine. The healthy urine of man is acid, owing 

 to the presence of acid sodium phosphate, the absence of free acid 

 being shewn by the fact that sodium hyposulphite gives no pre- 

 cipitate. The amount of acidity is about equivalent to 2 grms. 

 of .oxalic acid in twenty-four hours, but the degree of acidity at any 

 one time varies much during the day, being in an inverse ratio to 

 the amount of acid secreted by the stomach; thus it decreases 

 after food is taken, and increases as gastric digestion becomes 

 complete. It varies with the nature of the food; with a vege- 

 table diet the excess of alkalis secreted leads to alkalinity, or 

 at least to diminished acidity, whereas this effect is wanting with 

 an animal diet, in which the earthy bases preponderate. Hence 

 the urine of carnivora is generally very acid, while that of herbivora 



