FATS, PHOSPHATIDS, AND ALLIED SUBSTANCES 71 



10 drops of acetic anhydride and 2 drops of concentrated sul- 

 phuric acid are added. A violet color appears which quickly 

 turns to a blue green. 



Cholesterol is an important substance physiologically. Ap- 

 parently it protects the red blood corpuscles from certain harm- 

 ful substances. It also seems to exert a restraining influence 

 on some of the cell enzymes, and thus may act as a regulator of 

 some of the cell activities. Cholesterol and certain of its allied 

 substances are important in giving the cell its property of re- 

 taining the water which it contains. The presence of choles- 

 terol in the brain in such large quantities points to the suggestion 

 that it may have some important role in the functioning or 

 properties of this most important organ. In short, there are 

 doubtless numerous other roles played by cholesterol in the body, 

 of which we know very little as yet. 



