46 PHYSIOLOGICAL CHEMISTRY. 



opalescent solution. This is especially characterized by a 

 strong action on polarized light, [a] D = -f- 196 to 213, 

 according to different authorities. Like common starch gly- 

 cogen is a reserve material, being formed from the absorbed 

 sugar of the digestive process, and, in turn, being reconverted 

 into sugar from the liver as this is required for oxidation in 

 the body. After death the store of glycogen in the liver rap- 

 idly diminishes, glucose being produced. The amount of gly- 

 cogen present in the liver varies greatly with the diet and time 

 after eating. It may make up 12 to 16 per cent of the total 

 weight of the organ, but is usually much below this, perhaps 

 in the mean 2 to 3 per cent. In addition to its occurrence in 

 the liver glycogen is found in variable amount in the muscles, 

 and in traces in other body tissues. It occurs also in the vege- 

 table kingdom, and has been recognized in certain fungi. The 

 laboratory production of glycogen and some of the simple 

 reactions are illustrated by the following experiments, while 

 the physiological relations will be reserved for further discus- 

 sion in a later chapter. 



Ex. Kill a rat or a rabbit; remove the liver as quickly as possible, and 

 without delay cut it into small bits, which throw into a vessel of boiling" 

 water. The weight of the water should be about five times that of the 

 minced liver. Boil five minutes, then remove from the water and rub up 

 in a mortar with fine clean quartz sand. In this way the fragments of 

 liver become thoroughly disintegrated. The contents of the mortar, sand 

 as well as liver, are thrown into boiling water again and kept at 100 15 

 minutes. At the end of this time enough dilute acetic acid must be added 

 to impart a faint acid reaction. This coagulates and precipitates some 

 albuminous matters, which are separated when the hot mixture is filtered. 

 In the opalescent filtrate, which must be collected in a cold beaker, a fur- 

 ther precipitation of albuminous matter is effected by adding a few drops 

 of hydrochloric acid and some potassium mercuric iodide as long as a 

 precipitate forms. 



Filter again and use the dilute aqueous solution of glycogen resulting" 

 for tests below. 



Ex. Evaporate about half of the liquid above to a small volume and 

 precipitate impure glycogen as an amorphous white powder by addition of 

 strong alcohol. 



Ex. Add a little tincture of iodine to a small portion of the solution, 

 and note the red color produced. This color is discharged by heat Boil 



