1242 PHYSIOLOGY 



is generally turbid from the presence of precipitated earthy phos- 

 phates. In determining the reaction of urine it is usual to adhere 

 to one indicator, e.g. phenolphthalein, and to give the acidity in 

 terms of decinormal acid, naming the indicator used. The acidity 

 (i.e. the concentration of H ions) can also be determined by the 

 electrical method. In this way Hoeber found the acidity of human 

 urine to vary between 4' 7 X 10~ 7 and 100 X 10~ 7 . On the average it 

 was 49 x 10~ 7 in the litre. 



THE AVERAGE COMPOSITION OF THE URINE. Several analyses 

 of the day's urine under varying conditions of food have already been 

 given (v. pp. 855, 880). The following may be taken as a fair average 

 for an adult man on ordinary mixed diet : 



Total amount of urine = 1500 c.c. 



This contains about 60 grm. of salts, of which 25 grm. are inorganic 

 and 35 grm. organic. These are distributed as follows : 



INORGANIC CONSTITUENTS ORGANIC CONSTITUENTS 



Sodium chloride . . 15-0 grm. Urea . . . 30-0 grm. 



Sulphuric acid . . .2-5 Uric acid . . . 0-7 

 Phosphoric acid . . 2-5 



Creatinine . .1-0 



Hippuric acid . . 0-7 

 Other substances 2-6 



Potassium . 3-3 



Ammonia . . .0-7 



Magnesia . . . .0-5 



Lime . .0-3 



Other substances . . 0-2 



The quantity of urine will naturally vary with the water leaving 

 the body by the kidneys, and therefore according to the habit of the 

 individual with regard to the intake of fluids and with his occupation. 

 Thus after copious sweating the total amount may fall to 400 c.c. 

 in the course of the day. If large draughts of liquid be taken it may 

 rise to 3000 c.c. or more. There are also diurnal variations in the 

 amount secreted, depending probably largely on the circulation 

 through the kidneys. The secretion is at a minimum during sleep, 

 and especially between 2 and 4 o'clock in the morning. It is at its 

 maximum during the first hours after rising, and increases generally 

 after each meal. Muscular exercise may also give an initial increase 

 owing to the greater vigour of the circulation associated with exercise. 

 If the exercise is severe enough to cause sweating or is carried to 

 fatigue, there may be a consequent diminution in the amount of urine 

 secreted. 



THE INORGANIC CONSTITUENTS OF THE URINE 

 (a) ACID RADICALS. The chlorides of the urine are derived 

 almost entirely from the chlorides of the food. Though essential con- 



