686 ANIMAL PHYSIOLOGY. 
chlorinated lime to some urine to which an equal bulk of strong hydro- 
chloric acid has been added. Unless great care is employed in mixing 
up the fiuids, in the drop-by-drop addition of the solution of chlorinated 
lime, the indigo-blue will be oxidized (bleached) to indigo-white. 
The substance is soluble in chloroform which, being heavy, falls to 
the bottom of the glass and carries with it the indigo. 
Indol. C.H:N. 
A substance to which the odor of feces is in part due. It occurs in 
artificial and natural pancreatic digestion as a product of the action of 
bacteria. It is crystalline, soluble in boiling water, alcohol, and ether. 
Its alcoholic solution when nitrous acid is added gives a red color and 
its aqueous solution a red precipitate. 
Skatol. C.HoN (2). 
A substance occurring under the same circumstances as indol. It 
does not give the same reactions with nitrous acid as indol, but gives a 
violet-red color, when in urine, on the addition of concentrated hydro- 
chloric acid. It may, like the preceding, be obtained in crystalline 
form. 
NITROGENOUS METABOLITES. 
As may be gathered by a perusal of the chapter on the metabolism 
of the body, the nitrogenous metabolism, while most interesting and 
important, presents problems which as yet are in great part unsolved. 
However, something more of the nature of certain nitrogenous chemical 
compounds, either occurring in the body or related to such as are present, 
may now be considered with advantage. 
7 NH: 
Urea. CO NE. 
Urea may be regarded as the most important and: by far the most 
abundant solid of the urine of man and many other mammals, includ- 
ing practically, so far as known, all the carnivora and several other 
groups. It also occurs to a slight extent in the urine of birds. It is 
found in small quantity in blood and many of the fluids of the mam- 
malian body, though not at all or to but the smallest extent in muscles. 
It may be prepared from urine and obtained in colorless needles, soluble 
in water and alcohol, but not in anhydrous ether. When urine decom- 
poses, urea, possibly under the action of a ferment, becomes ammonium 
carbonate: 
Cont: 4. H.0 = (NH;):CO:. 
Urea may be made in the laboratory in several ways, some of which are 
indicated in the following equations: 
1. By heating ammonium carbonate: 
coche = CONH. + H.0. 
2. By heating ethyl carbonate with ammonia: 
COC er + INH, = CONsH: + 2C2H60. 
