328 PHYSIOLOGICAL CHEMISTRY. 



tain small amounts of iron and often traces of copper. But 

 the iron found is far from accounting for the amount which 

 must be separated from the hematin in the formation of bili- 

 rubin. In a former chapter the preparation of cholesterol from 

 gall-stones was described, also the general chemical behavior 

 of the substance. The character of a stone is most easily rec- 

 ognized by its behavior toward boiling alcohol, in which 

 cholesterol is rather readily soluble, to crystallize in large thin 

 plates on cooling. 



The solutions of cholesterol have a marked action on polar- 

 ized light, which property may be employed sometimes in the 

 identification and estimation. The specific rotations below 

 have been found. 



Ether solution c = 2 [a] JJ = 31.12 



Chloroform solution " 2 " 37.02 



" 5 " -37-81 



" 8 " 38.63 



In feces a modified cholesterol is found which has been called kopros- 

 terin and also stercorin. This new substance is a reduction product with 

 the probable formula C 2 7H4 8 O and is dextrorotatory, [a] -j- 24. 



Besides the two principal pigments several derived substances have been 

 obtained from the gall-stones. The following have been described: bili- 

 fuscin, biliprasin, bilihumin, bilicyanin. These substances exist in small 

 amount and are without practical importance. Their relations to the 

 others are not clearly established. 



