APPENDIX. 335 



Biliprasin is a pigment of a green color, which can be obtained from 

 gall stones. 



Bilihumin (Staedeler) is a dark brown earthy-looking substance, of 

 which the formula is unknown. 



Urobilin occurs in bile and in urine, and is probably identical with 

 stercobilin, which is found in the faeces. 



Uroerytlirin is one of the coloring matters of the urine. It is orange 

 red, and contains iron. 



Melanin is a dark brown^or black material containing iron, occurring 

 in the lungs, bronchial glands, the skin, hair, and choroid. 



HcB-matin has been fully treated of in Chapter IV. 



Indican is supposed to exist in the sweat and urine. It has not, how- 

 ever, been satisfactorily isolated. 



Indigo, C 8 H 5 N 9 0, is formed from indican, and gives rise to the 

 bluish color which is occasionally met with in the sweat and urine. 



Indol, Op H 2 N, is found in the faeces, and is formed either by decom- 

 position of indigo, or of the proteid food materials. It gives the charac- 

 teristic disagreeable smell to faeces. 



(4.) Nitrogenous Bodies of Uncertain Nature. 



Ferments are bodies which possess the property of exciting chemical 

 changes in matter with which they come in contact. They are at present 

 divided into two classes, called (1) organized, and (2) unorganized or 

 soluble. (1.) Of the organized, yeast may be taken as an example. Its 

 activity depends upon the vitality of the yeast cell, and disappears as soon 

 as the cell dies, neither can any substance be obtained from the yeast 

 by means of precipitation with alcohol or in any other way which has the 

 power of exciting the ordinary change produced by yeast. 



(2.) Unorganized or soluble ferments are those which are found in 

 secretions of glands, or are produced by chemical changes in animal or 

 vegetable cells in general; when isolated they are colorless, tasteless, 

 amorphous solids soluble in water and glycerin, and precipitated from the 

 aqueous solutions by alcohol and acetate of lead. Chemically many of 

 these are said to contain nitrogen. 



Mode of action. Without going into the theories of how these unor- 

 ganized ferments act, it will suffice to mention that: 



(1.) Their activity does not depend upon the actual amount of the 

 ferment present. (2.) That the activity is destroyed by high tempera- 

 ture, and various concentrated chemical reagents, but increased by 

 moderate heat, about 40 C. and by weak solutions of either an acid or 

 an alkaline fluid. (3.) The ferments themselves appear to undergo no 

 change in their own composition, and waste very slightly during the 

 process. 



Varieties. The chief classes of unorganized ferments are: 



(1.) Amylolytic, which possess the property of converting starch into 



