NERVOUS TISSUE. 251 



hours. The cold ether will extract lecithin and cholesterol. Filter 

 and add acetone to the filtrate to precipitate the lecithin. Filter 

 off the lecithin and test it as follows : 



(a) Microscopical Examination. Suspend a small portion in a 

 drop of water on a slide and examine under the microscope. 



(b) Osmic Acid Test. Treat a small portion with osmic acid. 

 What happens? 



(c) Acrolein Test. Make the acrolein test according to direc- 

 tions on page 135. 



(d) "Fusion" Test for Phosphorus. Place some of the leci- 

 thin prepared above in a small porcelain crucible, add a suitable 

 amount of a fusion mixture composed of potassium hydroxide and 

 potassium nitrate (5:1) and heat carefully until the resulting 

 mixture is colorless. Cool, dissolve the mass in a little warm water, 

 acidify with nitric acid, heat to boiling and add a few cubic centi- 

 meters of molybdic solution. In the presence of phosphorus a 

 yellow precipitate forms. What is it? 



2. Preparation of Cholesterol. Place a small amount of mac- 

 erated brain tissue under ether and stir occasionally for one hour. 

 Filter, evaporate the filtrate to dryness on a water-bath and test 

 the cholesterol according to directions given below. (If it is de- 

 sired, the ether extract from the so-called protagon, or the ether- 

 acetone filtrate from the lecithin may be used for the isolation of 

 cholesterol. In these cases it is simply necessary to evaporate the 

 solution to dryness on a water-bath.) Upon the cholesterol pre- 

 pared by either of the above methods make the following tests : 



(a) Microscopical Examination. Examine the crystals under 

 the microscope and compare them with those in Fig. 42, page 159. 



(b) Iodine-Sulphuric Acid Test. Place a few crystals of chol- 

 esterol in one of the depressions of a test-tablet and treat with a 

 drop of concentrated sulphuric acid and a drop of a very dilute solu- 

 tion of iodine. A play of colors, consisting of violet, blue, green 

 and red, results. 



(c) The Liebermann-Burchard Test. Dissolve a few crystals 

 of cholesterol in 2 c.c. of chloroform in a dry test-tube. Now 

 add 10 drops of acetic anhydride and 1-3 drops o'f concentrated 

 sulphuric acid. The solution becomes red, then blue, and finally 

 bluish-green in color. 



means of a freezing mixture. By this procedure both protagon and choles- 

 terol are caused to precipitate. Filter the cold solution rapidly and treat the 

 precipitate on the paper with ice cold ether to dissolve out the cholesterol. The 

 protagon may now be redissolved in warm 85 per cent alcohol from which 

 solution it will precipitate upon cooling. 



