NERVOUS TISSUES. 41 



Cerebrin is usually prepared according to the following 

 procedure: A small amount of the finely divided brain-tissue 

 is boiled for one-half hour in a casserole with twice its weight 

 of baryta-water. The solution is filtered off and the residue 

 extracted with boiling 95 per cent alcohol. From this 

 extract, if filtered while still hot, the cerebrin will separate 

 in small crystals. The cholesterol should stay in the alco- 

 holic solution, but if any becomes insoluble with the cere- 

 brin it is easily removed by washing the precipitate with 

 ether in the filter. 



Test the substance as follows: 



(a) Try to detect the presence of nitrogen and phos- 

 phorus. 



(6) Boil some of the substance for one hour with 5 per 

 cent H 2 S0 4 . After cooling the mixture, neutralize it and 

 test for a reducing action on Fehling's solution. 



(c) Warm some of the substance on a platinum foil. 

 Notice the odor. To what is it similar? 



THE CHOLESTEROLS. 



These bodies belong to the class of primary cell con- 

 stituents. They are studied here on account of the existence 

 of suitable material at hand. Cholesterol usually exists 

 free, as in the case of the brain-tissue and gall-stones, but it 

 is -also found in combination with fatty acids, as esters in 

 the blood-plasma. The best known cholesterol is a mon- 

 atomic alcohol with C 27 H 45 OH as the empirical formula. At 

 one time it was termed a " non-saponifiable " fat. It has 

 the general solubilities of the fats and crystallizes readily 

 from an alcohol or ether solution in the form of superimposed 



