442 PHYSIOLOGICAL CHEMISTRY. 



100 C. (212 F.). The residue is extracted with absolute alcohol, the filtered 

 alcoholic solution is again partially evaporated, and mixed with 10 volumes of 

 absolute ether. The biliary acids are soluble in alcohol, but not in ether, or 

 in ether containing one-tenth of alcohol. After standing an hour or two the 

 biliary acids will form a deposit, which is collected on a small filter, dissolved 

 in a little water, and mixed with a few drops of a strong solution of sugar. 

 Upon the addition of sulphuric acid, with the precaution above mentioned, the 

 characteristic colors will indicate the presence of the bile acids. 



Experiment 67. Evaporate ox-bile to a thick syrup, digest it with 5 parts of 

 pure, cold alcohol for two hours, and filter. Mix the filtrate, which contains 

 sodium glycocholate and taurocholate, with freshly prepared animal charcoal, 

 boil and filter ; evaporate to dryness in a water-bath, redissolve in the smallest 

 possible amount of pure alcohol, and add ether until the solution becomes 

 markedly turbid. A white, crystalline mass is deposited in a few hours or days ; 

 this is known as Plattner's crystallized bile, and is a mixture of the two sodium 

 salts mentioned. 



Dissolve the mass in a small volume of water, adding a little ether and then 

 dilute sulphuric acid; glycocholic acid crystallizes out in shining needles. 



Cholesterin, C 26 H 43 .OH. This substance has been classed by 

 physiologists among the fats, because it is greasy and soluble in 

 ether, but its chemical constitution is that of an alcohol. It is found 

 chiefly in bile, but also in blood, nerve-tissue, brain, contents of the 

 intestines, feces, etc. ; its presence in certain vegetables, as peas, beans, 

 etc., has also been demonstrated. 



Cholesterin crystallizes in colorless, silky needles, which are insolu- 

 ble in water, alkalies, and dilute acids, but soluble in ether. It 

 sometimes forms in the organism solid masses, known as biliary cal- 

 culi or gall-stones, some of which are almost pure cholesterin. 



Tests for cholesterin: 



1. Evaporated with nitric acid it gives a yellow mass, which turns 

 brick -red on addition of ammonia. 



2. Mixed in the dry state with strong sulphuric acid, it produces 

 a blue-red or violet color on addition of chloroform, the color chang- 

 ing to green on exposure to air. 



3. Evaporated with a mixture of 2 volumes of sulphuric acid and 

 1 volume of ferric chloride solution, it turns violet. 



Lecithins, C 44 H 90 NPO 9 or C 42 H 84 NPO 9 . Lecithin, one of the con- 

 stituents of bile, is a member of the group of substances generally 

 termed phosphorized fats or lecithins. These bodies are highly com- 

 plex in composition, and may be looked upon as fats formed from 

 glycerin, in which hydrogen atoms are replaced by the radicals of 

 phosphoric and fatty acids. 



