PHYSIOLOGICAL CHEMISTKY 319 



Like the lecithins it is very widely distributed in the animal body. 

 In the free state, it is present in the envelope and stroma of the red 

 blood corpuscles ; as an ester-, it is present in the blood serum. It is 

 also present in bile, and it may separate out from this to form calculi, 

 following a catarrhal state of the mucosa of the bile ducts. A variety 

 of cholesterol, called isocholesterol, is found in lanolin (purified wool 

 fat). Although we do not know much about its functions in the 

 animal body, yet there are indications that these must be important. 

 Thus, if added along with lecithin to a suspension of red blood cor- 

 puscles, it prevents haemolysis. It also antidotes the haemolytic action 

 of saponin. (See p. 462.) 



ADVANCED EXPERIMENT. Preparation of Cholesterol from Gall-Stones. 



The gall-stones are finely ground and boiled with 95 per cent, alcohol. The 

 alcoholic extract is filtered hot and allowed to cool, when crystals of cholesterol 

 separate out and can be filtered off, preferably with suction, using a perforated 

 porcelain plate fitted in a glass funnel and covered with a disc of filter paper. The 

 crystals are washed with a little cold alcohol, and may be re-crystallised from hot 

 alcohol. 



ADVANCED EXPERIMENT. Preparation of Cholesterol from Tissues, e.g. 

 Brain. The tissue is minced and then ground in a mortar with sand and about 

 three times its weight of plaster of Paris. After standing for some hours the 

 mass, which has now set hard, is ground in a mortar and cold acetone gradually 

 added. This extracts the cholesterol alone. The acetone is filtered and the 

 extraction repeated three times. On evaporation of the extract almost pure choles- 

 terol is obtained. This may be re-crystallised from hot alcohol. (Rosenheim.) 



Cholesterol is recognised by a number of colour reactions, of which 

 the most important are described in the following experiments : 



EXPERIMENT IX. Place some cholesterol crystals on a microscopic 

 slide and distribute them with a glass rod, and examine under the 

 microscope ; or better, dissolve some in absolute alcohol, place a drop 

 of the solution, on a slide, and allow it to evaporate. The crystals are 

 colourless, glancing rhombic plates having usually a square piece 

 removed from one corner. (Fig. 226.) The crystals give distinctive 

 colour reactions. 



Place some cholesterol crystals under a cover slip on a microscopic 

 slide, and allow a drop or so of a mixture of 5 parts sulphuric acid 

 (cone.) and 1 part water to run under the cover slip. Note that the 

 edges of the crystals become red. Now run in a drop of iodine solution, 

 when it will be noted that a play of colours results (brown, violet, blue, 

 etc.). 



Other colour reactions can be obtained with solutions of cholesterol. 



EXPERIMENT X. Dissolve some cholesterol crystals in a few c.c. 

 of chloroform, and add an equal volume of sulphuric acid (cone.). 



