470 EXCRETION 



SECTION 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. 24). 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 1,200 to 

 i ,600 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 solu- 

 tion of urea and inorganic salts, the proportion of the latter being 

 generally about 1-5 per cent., or double the usual amount of physio- 

 logical liquids. Besides urea, there are other nitrogenous bodies 

 in much smaller quantity, such as ammonia, uric, acid, and the 

 allied purin bases, hippuric acid, and kreatinin. Some of these at 

 least are products of the metabolism of proteins within the tissues. 

 And besides the inorganic salts there are certain organic bodies 

 indoxyl, phenyl, pyrokatechin', skatoxyl united with sulphuric 

 acid, which are primarily derived from the products of the putre- 

 faction 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 consisted 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 deter- 

 minations 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 1,487 c.c. 

 (for seven days), and the lowest 743 c.c. (for eight days). The greatest quan- 

 tity passed in any one period of twenty-four hours was 2,286 c.c. (by the in- 

 dividual 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. 



