514 THE NERVOUS SYSTEM. 



which conduct themselves towards iodine like cellu- 

 lose, but are essentially cholesterin (p. 480). 



The spinal marrow and the nerves, that have their 

 origin in it and in the brain, have a similar structure. 



100 parts of fresh human brain, dried at 100, leave 

 behind 21.5 parts of solid residue. 



The characteristic ingredient of the brain substance 

 is lecithin (protagon). To separate it, brain substance, 

 freed as thoroughly as possible from blood and cover- 

 ings, is reduced to a pulp, and shaken with water and 

 ether. The mixture is allowed to stand at 0, until 

 the ethereal solution appears at the top ; this is then 

 removed, and this process repeated several times, the 

 greater portion of the cholesterin being removed in 

 this way by the ether, while the ingredients, which are 

 easily soluble in water, remain dissolved in this sol- 

 vent. The ether and water are then filtered off as 

 thoroughly as possible, and the residue digested with 

 85 per cent, alcohol at 45 over a water bath, and 

 filtered while still warm. This solution, when cooled 

 down to 0, throws down an abundant precipitate, 

 which is collected and washed with ether until choles- 

 terin can no longer be detected in the filtrate. The 

 residue is dried in a vacuum over sulphuric acid, then 

 moistened with a little water and dissolved in alcohol 

 at 45. By gradual cooling of the filtered solution, 

 protagon is deposited in crystals, which may be puri- 

 fied by recry stall ization. 



It forms fine, radiate needles ; after drying over sul- 

 phuric acid, a light, flocculent powder. Difficultly 

 soluble in cold alcohol and cold ether, more easily in the 

 warm liquids. When heated with absolute alcohol to 

 a temperature higher than 55, it is dissolved, under- 

 going at the same time partial decomposition. "When 

 treated with water it swells up, forming an opaque, 

 pasty mass, which, with more water, yields a clear but 

 opalescent solution, from which protagon is precipi- 

 tated as a flocculent mass by boiling with concentrated 

 solutions of calcium and sodium chlorides and other 

 salts. It dissolves in glacial acetic acid, and crystal- 

 lizes from this solution unchanged, on cooling. 



