EXCRETION BY THE KIDNEY. 423 
Color—A light straw color, which is also very variable, 
being increased in depth either by the presence of an excess of 
pigment or a diminution of water. There are probably several 
pigments, among which occur wurobilin, derived probably from 
bile pigment; urochrome, becoming red on oxidation; and 
indican, which may be oxidized to indigo, 
The reaction of human urine is acid, owing to acid salts, espe- 
cially acid sodium phosphate (NaH,POQ,). There is usually but 
a trifling quantity, if any, of free acid in the urine when 
secreted. The acidity diminishes after meals, and the urine 
may be neutral or alkaline when the food is wholly vegetable, 
or unduly acid when the diet is entirely fleshy. 
Quantity.—Usually about 1,500 c.c. or from 50 to 52 ounces 
(two pints) in twenty-four hours. This is, of course, like the 
specific gravity, highly variable, and frequently they run par- 
allel with each other. 
The following tabular statement will prove useful for refer- 
ence: 
Quantitative Estimation of the Constituents of the Urine for 
Twenty-four Hours (after Parkes). 
By an average Per 1 kilo of 
man of 65 kilos. | body weight. 
Grammes. Grammes. 
Waters disec peadadaeeac ee eaeemen saneaeeny 1500-000 23-000 
Total solids. 55.05% wacigs uses bis CGA CoRR E SEE Rela a's 72-000 1:1000 
Urea...... Mostwadeeeagas aus Raiemieesys es eee 33°180 5000 
UTC acid cecsakcesecancs svesaetigine Seeeeiaes 565 0084 
Hippuriea0id. seicsesexcsvecereles 9% genes eews “400 0060 
Creatinit sss. 5:53 sch oy dere deo ooe he oy See eS 910 0140 
Figment, Ores wadenwetys GepecedeneSexewens 10-000 1510 
Sulphuric: acid. 2.:5¢%seches eres bse ieee ee geen 2012 0305 
Phosphoric acid................. Saeed cass 3°164 0480 
Chlorine: dans es 9 ey cash ewes seaedasdadeeanees 7-000 +1260 
AMMONIA: vex ce oy pees yedbes Cece Raye sakes 770 
Potassiuiny sicseae sed wean dee ago ee ase She ese 2500 
SOGUMvaacees Mees Veta sKES eeaNGRene susie 11-090 
Calcium. :s2sccses sedhei gate caneeyes 260 
Magnesium « :. 2026 scecsteaseecaseessinesnrcses 207 
Attention is directed more particularly to the preponderance 
among the solids of urea, and sodium chloride, for the latter is 
the form in which a large part of the sodium reappears. We 
may say that in round numbers about 35 grammes or 500 grains 
(2 to 3 per cent) of urea are excreted daily. 
Nitrogenous Crystalline Bodies—These are the derivatives of 
the metabolism of the body, and not in any appreciable degree 
drawn from the food itself. Besides urea, and of much less 
