LESSON XIII 

 CARBOHYDRA TES 



1. Grlycogen. A rabbit which has been fed five or six hours previously 

 on carrots is killed by bleeding. The chest and abdomen are opened quickly 

 and a cannula inserted into the portal vein, and another into the vena cava 

 inferior. A stream of salt solution is then allowed to pass through the liver 

 until it is uniformly pale. The washings are collected in three beakers 

 labelled a, 6, and c. 



The liver is cut out quickly, chopped into small pieces, and thrown into 



boiling water acidulated 

 with acetic acid. The 

 acidulated water extracts 

 a small quantity of glyco- 

 gen. The pieces of scalded 

 liver are then ground up 

 Sin! in a mortar with hot 



water, and thoroughly 

 extracted with boiling 

 water. Filter. A strong 

 solution of glycogen is 

 thus obtained. 



Test the solution when 

 cold with iodine. 



To separate the glyco- 

 gen evaporate the solu- 

 tion to a small bulk on the 

 water-bath and then add 

 excess of alcohol ; the 

 glycogen is precipitated 

 as a flocculent powder, 



which is collected on a filter and dried in an oven at the temperature of 100 



(see fig. 55). 



If the experiment is to be a quantitative one ; the piece of liver taken and 



the glycogen obtained must be weighed. 1 



2. Examine the washings of the liver in the beakers a, b, and c for sugar. 

 This may be done in a rough quantitative manner as follows : Take equal 



1 This method of preparation of glyeogen has the advantage that only traces 

 of protein are mixed with it. In Kiilz's method (extraction with dilute potash) 

 there is more protein. This is precipitated by the alternate addition of hydro- 

 chloric acid and potassio-mercuric iodide. Pavy and also Pfliiger recommend 

 extraction with strong potash, and subsequent precipitation with a certain per- 

 centage of alcohol ; this method extracts all the glycogen easily. 



FIG. 55. Hot-air oven with gas regulator (<;). (Gscheidlen.) 



