436 A MANUAL OF PHYSIOLOGY 



I. Excretion by the Kidneys. 



The Chemistry of the Urine. Normal urine is a clear yellow 

 liquid acid to litmus and similar indicators, but nearly neutral 

 or very weakly acid in the physico-chemical sense (p. 23). The 

 average specific gravity is about 1020, the usual limits being 1015 

 and 1025, although when water is taken in large quantities, or 

 long withheld, the specific gravity may fall to 1005, or even less, 

 or rise to 1035, or even more. The quantity passed in twenty- 

 four hours is very variable, and is especially dependent on the 

 activity of the sweat-glands, being, as a rule, smaller in summer 

 when the skin sweats much, than in winter when it sweats little. 

 The average quantity for an adult male is 1200 to 1600 c.c. (say, 

 40 to 50 oz.).* 



Composition of Urine. This is very closely related to the 

 quantity and quality of the food. Hence it is impossible to 

 speak of a definite normal composition of the urine. It is 

 essentially a solution of urea and inorganic salts, the proportion 

 of the latter being generally about 1-5 per cent., or double the 

 usual amount in physiological liquids. Besides urea, there are 

 other nitrogenous bodies in much smaller quantity, such as 

 ammonia, uric acid, and the allied xanthin bases, hippuric acid, 

 and kreatinin. Some of these at least are products of the 

 metabolism of proteins within the tissues. And besides the in- 

 organic salts there are certain organic bodies indoxyl, phenyl, 

 pyrokatechin, skatoxyl united with sulphuric acid, which are 

 primarily derived from the products of the putrefaction of 

 proteins within the digestive tube. 



Folin has published analyses of ' normal ' urines from six persons, 

 weighing from 56-6 to 70-9 kilos (average 63-4 kilos), who were 

 kept for seven days on one standard uniform diet. The diet con- 

 sisted of 500 c.c. of milk, 300 c.c. of cream (containing 1 8 to 22 per 

 cent, of fat), 450 grammes of eggs, 200 grammes of Horlick's malted 

 milk, 20 grammes of sugar, 6 grammes of sodium chloride, water 

 enough to make the whole up to two litres, and 900 c.c. of additional 

 water. The ingredients contained 119 grammes of protein, about 

 148 grammes of fat, and 225 grammes of carbo-hydrates. The 

 average results of all the determinations are given in the following 

 table : 



* The average quantity of urine varies not only with the season, but 

 also with the habits of the person, especially as regards the amount of 

 liquid taken. The average for seventeen healthy (American) students, 

 whose urine was collected for six to eight successive days in winter, was 

 1 166 c.c. The highest average in any one individual for the observation 

 period was 1487 c.c. (for seven days), and the lowest 743 c.c. (for eight 

 days). The greatest quantity passed in any one period of twenty-four 

 hours was 2286 c.c. (by the individual whose average was the highest). 

 The smallest quantity passed in twenty-four hours was 650 c.c. (by the 

 individual whose average was the lowest). 



