252 PHYSIOLOGICAL CHEMISTRY. 



(d) Salkowski's Test. Dissolve a few crystals of cholesterol in 

 a little chloroform and add an equal volume of concentrated sul- 

 phuric acid. A play of colors from bluish-red to cherry-red and 

 purple is noted in the chloroform, while the acid assumes a marked 

 green fluorescence. 



(e) Schiff's Reaction. To a little cholesterol in an evaporating 

 dish add a few drops of Schiff's reagent. 1 Evaporate to dryness 

 over a low flame and observe the reddish-violet residue which 

 changes to a bluish-violet. 



(/) Phosphorus. Test for phosphorus according to directions 

 given on page 251. Is phosphorus present ? 



3. Preparation of Cerebrin. Treat the macerated brain tissue, 

 in a flask, with 95 per cent alcohol and boil on a water-bath for 

 one-half hour, keeping the volume constant by adding fresh alcohol 

 as needed. Filter the solution hot and stand the cloudy filtrate away 

 for twenty- four hours. (If the filtrate is not cloudy concentrate it 

 upon the water-bath until it is so.) Filter off the cerebrin 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) Solubility. Try the solubility of cerebrin in the usual sol- 

 vents and in hot and cold alcohol and hot and cold ether. 



(c) Phosphorus. Test for phosphorus according to directions 

 on page 251. How does the result compare with that on lecithin? 



(d) Place a little cerebrin on platinum foil and warm. Note 

 the odor. 



(e) Hydrolysis of Cerebrin. Place the remaining cerebrin in 

 a small evaporating dish, add equal volumes of water and dilute 

 hydrochloric acid and boil for one hour. Cool, neutralize with 

 solid potassium hydroxide, filter, and test with Fehling's solution. 

 Is there any reduction, and if so how do you explain it? 



4. Tests for Choline. (a) Rosenheinis Periodide Test. Pre- 

 pare an alcoholic extract of the fluid under examination, and after 

 evaporation, apply Rosenheim's iodo-potassium iodide solution 2 to 

 a little of the residue. In a short time dark brown plates and 

 prisms of choline periodide begin to form and may be detected by 

 means of the microscope. Occasionally they are large enough to 

 be visible to the naked eye. They somewhat resemble crystals of 



1 Schiff's reagent consists of a mixture of three volumes of concentrated sul- 

 phuric acid and one volume of 10 per cent ferric chloride. 



3 Prepared by dissolving 2 grams of iodine and 6 grams of potassium iodide 

 in TOO c.c. of water. 



