THE BRAIN. 141 



mentation lactic acid in that it rotates the plane of polarized light 

 toward the right. Fermentation lactic acid does not do this. 



316. Convert a part of the creatin into creatinin by boiling 

 fifteen minutes with very dilute sulphuric acid. Neutralize the 

 acid by adding powdered barium, carbonate as long as it effer- 

 vesces. Evaporate to dryness on a water-bath and extract the 

 creatinin from the residue with strong alcohol. Upon evaporat- 

 ing, the creatinin is left in the form of crystals. 



317. Dissolve a little of the creatinin in a small amount of 

 water, add a solution of zinc chlorid, and allow to stand. Charac- 

 teristic crystals in clusters or rosettes appear. They are a double 

 salt of creatinin and zinc chlorid. 



318. To a creatinin solution add a few drops of a freshly- 

 prepared solution of sodium nitroprussid, then, drop by drop, 

 dilute sodium hydrate. The liquid becomes ruby red, soon chang- 

 ing to straw color. If it is now strongly acidified with acetic acid 

 and boiled, it becomes green, then blue. This is WeyPs test. 



319. To a solution of creatinin add a few drops of sodium 

 hydrate, then of picric-acid solution. A red color is obtained. 

 This is Jaffe's test. 



320. With a needle tease out some shreds of muscle 

 from a recently killed frog. Place them on a microscope 

 slide and expose for a few minutes to ammonia gas from a 

 strong solution of the hydrate. When covered with a cover- 

 glass and examined they are seen to contain stellate crys- 

 stals of ammonium magnesium phosphate,, NH 4 MgP0 4 . 

 Explain its production. 



THE BEAIN. 



321. Clean the brain of a sheep, pig or calf, pulp in a mortar, 

 extract several hours with 88-per-cent. alcohol and filter. The 

 lecithin, cholesterin and the substance known as protagon pass 

 into the filtrate. Cool this to 5, when they solidify, then re- 

 move them by filtration. Dissolve the lecithin and cholesterin in 

 cold ether (danger from fire!). The so-called protagon remains. 

 After this has been dried fuse a portion with potassium nitrate 



