FUNCTIONS OF THE KIDNEY 83 



increases the urinary secretion. Children discharge 

 more urine than adults, and women, relatively more 

 than men. Even mental conditions affect the flow, as is 

 evidenced in hysteria when loss of nervous control enor- 

 mously increases the output. Diet largely affects both 

 the quantity and the contents; and, of course, the 

 amount of liquid taken will act even more decidedly and 

 more rapidly. Drinking a quantity of water will increase 

 the flow ; but drinking the same amount of beer will not 

 only cause a greater flow, but the increase will occur 

 earlier. Many drugs, called diuretics, produce the same 

 effect, while others will diminish the quantity. 



Composition of Urine. Urine holds a large number 

 of different bodies in solution, but is chiefly notable be- 

 cause it takes away the product of the digestion of ni- 

 trogenous food in the form mainly of urea. 



Urea is the most important nitrogenous element in 

 the urine. That urea, or some antecedent substance, is 

 formed largely in the liver seems certain. It is present 

 in the blood and other tissues and so large a part of the 

 total output is removed by the kidneys that the removal 

 of both of these organs ahvays causes death. The aver- 

 age amount excreted in twenty-four hours is from 350 

 to 450 grams. Drinking large quantities of water will 

 decrease the relative but increase the actual amount of 

 urea, while an increase in nitrogenous food increases, 

 and of vegetable food, diminishes, the output of urea. 

 Exercise, or anything which increases metabolism of tis- 

 sue, increases the amount of urea. 



Uric acid as such does not occur in urine in health, 

 but in the form of urates, chiefly of sodium though sim- 

 ilar salts of potash, lime, magnesia and ammonia are 

 found. From ten to fifteen grains of urates are ex- 

 creted daily. They are not formed in the kidneys, but 



