CHEMICAL COMPOSITION OF THE HUMAN BODY 23 



envelopes of the Tunicates. A gum-like carbohydrate can be split 

 off from certain mucins (animal gum). 



Glycogen is chiefly found in the liver and muscles. It is 

 formed, first of all, by the anhydrid union of several mole- 

 cules of the simple sugar, chiefly of dextrose, but also of 

 levulose and galactose. Glycogen can also be formed from 

 proteids. 



Glycogen is dextrorotatory; boiling with acids splits it up 

 into dextrose only, hence in the formation of glycogen from 

 levulose and galactose, these must first be changed to dex- 

 trose. 



Glycogen forms an opalescent solution in water and is 

 precipitated by the addition of half its volume of alcohol. 

 It does, not reduce nor ferment and, with iodine potassium 

 iodide, gives a brownish-red color which disappears on heat- 

 ing. Ferments (diastase, ptyalin) split it up, under the 

 assumption of water, into maltose and dextrose, dextrins 

 being intermediate products. 



The object of glycogen formation in the animal body is 

 the storing up of carbohydrates in a form which, under the 

 given conditions, is insoluble (like the sugar in plants is 

 stored up as starch). 



2. Fats are fatty acid _esters_of glycerin. The most im- 

 portant fatty acids which take part in ester formation are : 



Palmitic acid, C 15 H 31 COOH; 

 Stearic acid, C^H^COOH; 

 Oleic acid, C 17 H 33 COOH. 



Glycerin as a triatomic alcohol can unite with three mole- 

 cules of fatty acid : 



/OH /0(C 16 H 31 0) 



C 3 H 5 -OH + 3 C 15 H 31 COOH = C 3 H 5 _O(C 16 H 31 O) + 3 H 2 O. 



\OH \0(C 16 H 31 0) 



The glycerin-esters of palmitic, oleic, and stearic acids are 

 called palmitin, olein, and stearin, and a mixture of these 

 three is what is commonly known as fat. 



The melting-point of stearin is 71.5, of palmatin 62, of 



