NERVOUS TISSUE 373 



was formerly called a " non-saponifiable fat" but since it is not changed 

 in any way by boiling alkalis it is not a fat. It is soluble in ether, 

 chloroform, benzene, and hot alcohol. It crystallizes in the form of 

 thin, colorless, transparent plates (Fig. 63, page 213). Cholesterol 

 is present in bile, and occurs abundantly in one form of biliary calculus. 

 It is also present in blood and its quantitative determination is of 

 clinical importance (see Chapter XVI). It has been found in feces, 

 wool fat, egg yolk, and milk, frequently in the form of its esters of 

 higher fatty acids. It is generally believed that the cholesterol present 

 in the animal body has its origin in the vegetable kingdom. Some 

 evidence has been submitted 1 indicating a synthesis of cholesterol 

 under certain conditions in the animal body. However, it is probable 

 that cholesterol is not readily synthesized in the body. 2 



Paranucleoprotagon is a phosphorized substance originally isolated 

 from brain tissue by Ulpiani and Lelli and recently reinvestigated by 

 Steel and Gies. It is said to possess lecithoprot^in characteristics. 



Nervous tissue yields about i per cent of ash which is made up in 

 great part of alkaline phosphates and chlorides. 



EXPERIMENTS ON THE LIPOIDS OF NERVOUS TISSUE 3 



1. Preparation of Lecithin. 4 Treat the finely divided brain of a sheep with 

 ether and allow it to stand in the cold for 48-72 hours. The cold ether will ex- 

 tract lecithin and cholesterol. Filter and add acetone to the filtrate to pre- 

 cipitate 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. 5 Treat a small portion with osmic acid. What 

 happens? 



(c) Acrolein Test. Make the acrolein test according to directions on page 

 184. 



(d) Test for Phosphorus. See page 128, Chapter VI. 



2. Preparation of Cholesterol. Place a small amount of finely divided 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 direc- 

 tions given below. (If it is desired, the ether extract from the so-called protagon, 



1 Klein: Biochem. Zeit., 30, 465, 1910. 



2 Gardner and Lander: Proc. Royal Soc.^ London (B), 87, 229, 1913. 

 ^Preparation oj So-called Protagon. Divide the brain of a sheep into small pieces, 



treat with 85 per cent alcohol and warm on a water-bath 45C. for two hours. Filter hot 

 into a bottle or strong flask and cool to oC. for one-half hour, by means of a freezing mix- 

 ture. By this procedure both protagon and cholesterol are caused to precipitate. Filter 

 the cold solution rapidly and treat the precipitate on the paper with ice cold ether to dis- 

 solve out the cholesterol. The protagon may now be redissolved in warm 85 per cent 

 alcohol from which solution it will precipitate upon cooling. 



4 For the preparation of lecithin in purer form see MacLeon: Jour. Path. Bact., 18, 490, 

 1914. 



6 Osmic acid serves to detect fats which contain un^atur ated fatty acid jradicals, e.g., 

 oleic add, in their molecule. 



